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  #1  
Old 10-03-2006, 08:49 AM
LDBennett
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AGI's modification for the 10/22 to 17HM2



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This is a contraversial subject as all forms of modifications have been tried with failures and successes as chronicled here on this site. Let there be no flaming and let all accept the information without throwing stones at me, AGI, or Bob Dunlap. Take the information for what it is worth to you or leave it, but here is an overview. Last months preview of this subject got removed by administration for flaming. Let's try to avoid this happening again, as it denies others of the presented information. Honest comments are welcome, flaming is not!

Introduction
Conversion of a Ruger 10/22 to 17HM2 is a very controversial subject, it seems, because a few on this site have literally years of experience trying to make it fool proof with failures and successes along the way that make those persons feel like experts. American Gunsmithing Institute (AGI) and Bob Dunlap, both with credential to make them masters of gunsmithing education and of gunsmithing took on the challenge, found the pitfalls and offered up a learned solution which may disagree somewhat with the “experts” on this site. I offer this overview of their solutions as presented to the AGI Inner Circle in AGI’s monthly DVD magazine.Remember this is a total solution and as such must be done in total, not piece meal.

Remove excessive chamfer of chamber in barrel:
The chamber chamfer at the breech end of the barrel should be minimal as that effects the ultimate headspace. Only the top and bottom of the chamber should have any at all and it should be light on the top and slightly more on the bottom. The sides should have no chamfer at all for maximum case support. The barrel should be faced off to achieve this and the extractor cut adjusted for extractor clearance with a resultant knife edge of chamber at the extractor cut.

Extractor cut on the barrel:
It is important that the bolt be full closed when the cartridge fires. The spring behind the extractor operating on the extractor cut on the barrel can force the bolt back out of battery if that cut is not radiused to match the forward facing end of the extractor. The method is a small grinding disk on a Dremel used judiciously to form the bottom of that cut for extractor clearance.

Bolt face cut for cartridge rim:
As the bolt fits very sloppy in the 10/22, the chances of the bolt being held slightly out of battery is high if the relief cut in the bolt face is not large enough for clearance around the rim of the cartridge in all instances. The 10/22 is partially assembled and the limits of the bolt vertical and horizontal out of perfect alignment closing are noted (using a cartridge whose rim has been marked with a magic marker) and the bolt face cut enlarge to accommodate that miss-alignment range. Again the tool of choice is the Dremel but with a small burr used only in the edge area of the bolt cut that shows such additional clearance is required.

Bolt headspace measured and adjusted:
The clearance between the bolt face and the rear of the cartridge should be no more than a few thousandths of an inch. The bolt face is shortened so the resultant cut depth of the bolt face is in the range of 0.044 to 0.046 inches. This results in 0.001 to 0.002 inches of clearance behind the chambered cartridge case. The method (controversial to me) is using a belt sander, making multiple passes by rotating the bolt to each of the four sides, repeatedly. (Dunlap has steady hands and years of experience so his came out perfect. I am not so sure I could do as well with this method. I’d try to find a better more accurate way?)

Heavy bolt handle:
Use of the heavy bolt handle may not be necessary if the above mods are made correctly. It turns out that eventually the heavy bolt handle will become problematical as the leverage the handle has on the cross piece that fits into the bolt cut is high. The inertia of the bolt handle is high and the mechanical advantage of the bolt mount low with the result that after a few rounds the bolt handle gets looser and looser in the bolt as either or both the bolt cut and the handle mount get beat up. Bob Dunlap suggests the above mods and try not using the heavy bolt handle. Only defer to its use with continued bulged or split cases and inspect and replace it as it grows looser with usage.
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  #2  
Old 10-03-2006, 09:55 AM
tfrank
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Talking Thank you, thank you, thank you.................

Got this info copied to a 17Mach2 folder. Thanks so much for your time and effort in sharing this info with us!!!! Contains a lot of minute detail that looks like it could make a real big difference in the way a rifle (pistol) will operate!!!
God Bless, Frank.
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  #3  
Old 10-03-2006, 11:51 AM
Markbo
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Interesting. Nothing more than some machining and touch up with no mention of spring tuning whatsoever. Interesting. Has Bob done any experimenting along those routes in order to avoid the heavy bolt handle issues?

One thing I don't quite understand if you could clarify please is the bolt face cut for cartridge rim - does that mean enlarging the bolt face for the diameter of the case to account for inherent bolt sloppiness?

If so, is this allowing a little movement within that bolt face so that the cartridge remains square in the chamber without undue force from the bolt not being perfect? I guess this looseness is not an issue so long as the headspace is accurate?

Anyone who can accurately square a bolt face by hand is a craftsman in my book!
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Old 10-03-2006, 12:11 PM
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Well, I guess I did it right after all. Bought one of the GM 17cal barrel deals awhile back and this seems to verify what I found when I made the conversion. Converted one 10/22 and it worked fine with just the magnum spring and bolt handle, but another had bulged cases almost looking like a belted case. On examination I found that that barrel had a large chamfer on the rear of the chamber. I changed that barrel for one that had no chamfer and the gun worked fine. Also this gun had a bolt with minimun headspace and the bolt face had been surfaced flat. Cases fly about 6ft on ejection and no bulges. Now if it was just more accurate.
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Old 10-03-2006, 03:39 PM
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Someone should tell Whistlepig.
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  #6  
Old 10-03-2006, 04:04 PM
LDBennett
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Markbo:
"One thing I don't quite understand if you could clarify please is the bolt face cut for cartridge rim - does that mean enlarging the bolt face for the diameter of the case to account for inherent bolt sloppiness?"

This cut was made to assure that the bolt did not hit the rim and remain every so slightly open (too much headspace). Seems the bolt can flop around and this insures the bolt is always fully closed at the time the gun is fired and not held slightly open by the edge of the rim hitting the bolt face cut.

In this presentation nothing was said about changing springs but if I get a chance I'll review the original conversion DVD and see if they had previously changed the springs. The conversion was made several months ago and after the DVD was sent out they had split cases start showing up. Bob Dunlap was fixing it from that point (?). My guess is that the springs were part of the original "kit". While Bob pointed out the different powder burning characteristics of 17HM2 he seemed to down play it and only pointed out that the faster burning opened the bolt sooner. From that he stated that the timing of opening was more critical than 22LR and that assuring the bolt was really closed at firing time and the headspace minimum (all of the mods he did) would reduce the possibility of blown cases. They are suppose to shoot it next month (?). Maybe more will come of it?????

LDBennett
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Old 10-03-2006, 05:50 PM
cletus hungwell

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the info posted seems more to me to be the basics for a match grade action job that have been openly discussed here for years, and have little to do w/ the problems specific to the hm2...there are several things that make me doubt the usefullness of this info, ie: heavy bolt handle probs???....it is spring loaded to the front, and under constant pressure even when worn....slack there would have no practical effect on action timing whatsoever unless done to an extreme

the problem in making a drop in kit for these is the hysterisis (sp?) of the bolt/action bein so different from gun to gun as to make "tuning" a requirement... i really don't see anyone resolving this issue w/o tuning for each action....there is just too much variation from gun to gun for this to happen...

just my opinion, as a non expert on rimfires.....but, i did design/build the first chopped m60mg's (now known as the E3 variant) anyone in special forces ever saw in '74-'75 at the weapons pool at fort bragg... 36" OAL, 12.5lbs if my memory is correct....

cletus
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  #8  
Old 10-04-2006, 07:56 AM
LDBennett
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cletus:

Indeed the information is to get the action to FULLY close every time. If the action is held open at all it opens sooner leaving the case unsupported earlier when the pressure is higher, bulging the cases. The example used was deemed "typical" so every 10/22 should be treated to these basic inspections and corrections. If the 17HM2 peaks faster then assuring the timing of opening is correct and never early is a bonified "fix". Apparently the 10/22 design is so crude that this is necessary for 17HM2 version but 22LR is just slow enough in the pressure peak that the crude timing of the "typical" one still works OK. Isn't it always the basics that make the most difference!

The bolt handle that was exhibited on the AGI 10/22 had 200 rounds on it. When compared to a brand new one it already had become somewhat loose in the bolt and showed real signs of being beat up. While not a part of the "17HM2" problem, it may become a problem of its own. It is just an observation of the "standard" fix used by so many so far. This is not the way to longevity in the reliability department. It gets beat up and the bolt too, with the eventual result that it stops the gun, breaks and flies off or ruins a perfectly good gun and a shooting session. I personally do not want to install parts that are known to be weak and/or a reliability issue. At a minimum if a person uses the heavy bolt handle that person needs to be aware of the reliability issue and inspect it regularly with the expectation that both the bolt and the handle may be damaged over time.

As I said in the Intro: take it or leave it. If you do not believe it, so be it. But at least consider the source and the info itself, then discard it if you wish. While it may not be revolutionary information it is learned information, none the less, and deserves consideration. Sometimes it is returning to the basics that solves problems!
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Old 10-04-2006, 11:44 AM
cletus hungwell

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thx for all the efforts in bringin this info to the forum....

i agree the basic problem is the short duration pressure spike that occurs in the early part of the cycle.... and you've reached the same conclusion i have re: the crudeness of the action requireing a complete redesign/rebuild to function properly w/ this little cartridge.....

his focusing on the head space issue seems to be an attempt to resolve the domed head problem....this has been chased down repeatedly here, by myself and many others...i still got it just as much after headspacing/etc....it has been shown in dozens of examples that while it is recommended, it doesn't do a huge amount to resolve this problem...

the best solution i've seen in print so far has been done by a couple of folks here.....installing a pair of spring loaded detents in the top of the trigger housing that engage a slot/divot in the bottom of the bolt......these are a bit tricky to install properly, if you're not used to using them in this type application,to get positive forward pressure @ battery, but are far more promising IMHO.....i personally think they would go along way for gettin the max out of the .22lr also.... i believe batman posted the last pics of this mod... others have used this mod to tame the .17hmr into the lr action... it's hard to argue w/ results....

keep us posted on what works in your gun
cletus
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Old 10-04-2006, 02:21 PM
Markbo
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I should be getting mine back from the smith with mine installed any day now. As soon as I get the opportunity, I will post results.

FYI LD, as Cletus already knows my initial attempts at solving the timing issue (which worked fine by the way) were nothing more than a very slightly overweight brass bolt handle and using different springs to find the magic combination. These included VQ and Power custom hammer springs and a shortened Ruger 22 magnum recoil spring. After trying lots of different combinations, I finally got MY sweet spot and it functioned flawlessly with only a very occasionally and slightly bulged head.

While the gun shot great (this is an inherently very accurate little round), I wanted 100% reliability make sure my accuracy didn't suffer so after batman's very nice write up, I am trying that as well. I believe that will solve the 'closed all the way every time' issue.
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Old 10-04-2006, 03:00 PM
cletus hungwell

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i think these rifles all benefit from proper timing, regardless of the cal used...

i've got a spring combo that just barely lays the aguilla 60gr short cases out onto the bench....the consistency of this has really improved the accuracy of this round in the 1-9 volq... low .2"s for [email protected] is the norm w/ it now with the occasional group goin to mid .1"s....considering i'm not much of a rifle shot, and am shooting off bipod/rear bag, i think it's acceptible

i would love to get a group set up w/ detents that were easily adjustible to allow the fine tuning for each load....with the new eley match eps showing such tiny SD on velocity, it should bring these little guns a touch closer to bolt gun accuracy potential....

i look forward to your normal thorough review/posts on your mod mark!!!!!...i allways enjoy them and find them informational.....

cletus
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Old 10-04-2006, 08:13 PM
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I am using the 96/17hm2 brl, .22mag bolt and return spring and PC hammer spring. The chamber is chamfered and have had no feeding problems. All fired cases are still flat faced but some cases have the bulge ring in front of the rim while others have none.

Since some cases are not bulging I would assume that the chamfer is not too much. Is the area in front of the rim a weak area of the case? It doesn't appear that the neck of the case is deformed on the cases that have backed out of the chamber.

I think I am correct that the rounds will eject without an extractor? If it is the extractor that is pushing the bolt back to allow the bulge then the problem should go away when it's removed. I'll give that a try. If that doesn't work then I will look at opening the bolt face.

I have not checked my headspace but since the base of the fired case if flat I'll assume the spacing is not a problem (unless the extractor is holding it back to the bolt, then it might show a problem with the extractor removed).

Comments? I've just been winging it from the info I have picked up from those who have gone before me.
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Old 10-05-2006, 08:13 AM
LDBennett
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Return Spring replacement for the AGI conversion:

I reviewed the DVD where AGI did the conversion and nothing specific was said about what or which spring or bolt handle was used. I would guess it is a set. Although Bob Dunlap does not mention changing the return spring, I believe it is necessary, at a minimum.



For those who have presummed that I was converting a 10/22, that is not the case. I am only reporting the progress, in that reguards, of AGI's Master Gunsmith Bob Dunlap in his effort to fix a case bulging conversion done by others on the AGI staff. This is important, I think, because it shows how a well educated gunsmith with decades and decades of both gunsmith education and gunsmith business ownership would tackle this kind of problem. Based on what I have read here and in seen in the AGI Inner Circle DVD, I believe that the 10/22 is the wrong vehicle for a 17HM2 conversion, as it is too crude to handle the pressure spike of the 17HM2. Some manufacturer needs to take this problem in hand and solve it by designing a completely new semi-auto gun specifically for the 17HM2 that incorporates enough safety of design that blown cases of any kind flat can not happen. To me it is not sufficient to minimise blown cases, which is where I think the AGI effort is going. They shoot the correctly head spaced 10/22 next month. We'll have to see where that takes us (???).
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Old 10-05-2006, 08:48 AM
cletus hungwell

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Quote:
Originally Posted by LDBennett
Return Spring replacement for the AGI conversion:

I reviewed the DVD where AGI did the conversion and nothing specific was said about what or which spring or bolt handle was used. I would guess it is a set. Although Bob Dunlap does not mention changing the return spring, I believe it is necessary, at a minimum.



For those who have presummed that I was converting a 10/22, that is not the case. I am only reporting the progress, in that reguards, of AGI's Master Gunsmith Bob Dunlap in his effort to fix a case bulging conversion done by others on the AGI staff. This is important, I think, because it shows how a well educated gunsmith with decades and decades of both gunsmith education and gunsmith business ownership would tackle this kind of problem. Based on what I have read here and in seen in the AGI Inner Circle DVD, I believe that the 10/22 is the wrong vehicle for a 17HM2 conversion, as it is too crude to handle the pressure spike of the 17HM2. Some manufacturer needs to take this problem in hand and solve it by designing a completely new semi-auto gun specifically for the 17HM2 that incorporates enough safety of design that blown cases of any kind flat can not happen. To me it is not sufficient to minimise blown cases, which is where I think the AGI effort is going. They shoot the correctly head spaced 10/22 next month. We'll have to see where that takes us (???).

can you post some links to pics of guns this bob duncan has designed/built???....i don't mean assembled from an action, barrel, and stock, but one he completely designed and built??? i'm kinda funny about folks claiming to be "masters" of an ancient and honorable craft such as smithing, and have seen way too many "master smiths" that have never built a single thing from scratch.....i'm not aware of any trade associations awarding journeyman/master's certification for gunsmiths in the usa at this time, so i wonder who's idea of a "master" he really is...

i'm not sayin he's not a competent mechanic, nor that he has never done quailty modifications, but callin someone a "master" calls for some "bona fides" in my book....

cletus
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Old 10-05-2006, 09:57 AM
Markbo
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LD, I also hope that you don't think we are throwing out alternatives because we don't think AGI or Bob Dunlap capable. I have some AGI tapes and know OF Bob Dunlap and I am 100% confident he knows his stuff.

I also know that some talented guys have been working on this stuff here too. Would you be so kind as to just pass on the information we have told you? You know Carbine Williams wasn't a Master Gunsmith when he started!

I am definitely not saying we know more than him or anything like that. I just think that some of the ideas our local engineers & machinists have come up with are very valid. I know MY 10/22 no longer has bulged case heads and has never had a case separation. Could that be made in a manufactured gun from Ruger? Not for anything like affordable. I like your idea of a 'new gun'. I have always thought that a single slug semi rotating bolt would be easy to do in a .22. Even 2 small lugs could work.

Then again one of the reasons for the 10/22's popularity in general and specifically for caliber change is it's modular design and easy nature to work on. Like Skeeter says here all the time, you can get any 10/22 to shoot 1/2" goups with enough effort. To get one to shoot 1/4" groups takes a LOT of work. To pay for that work from Ruger would make it too expensive to be attractive.
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