Rimfire Central Firearm Forum banner

Robert's 17HMR Magnum Build

16K views 147 replies 14 participants last post by  tanakasan 
#1 · (Edited)
Robert's 17HMR Razor Magnum Build

Well, I got the chance to machine my Razor receiver and bolt today!

Also, I was surprised at how light the recoil spring is!:eek: I have found a like sized replacement but with twice the rating. The SF spring is around 62# rating, the possible replacement is 124#.

Also going to machine a long brass follower. The SF follower is 5g, the joiner (not really coupled mass) is 3g. I am thinking that a 3" long follower should add a few grams to the bolt mass. SF charging handle by itself is 22g. Going to see how much mass I can add...can't hurt, right? I was surprised that brass is slightly more dense that stainless steel! Learn something every day!

I did not install my KID +10% spring. If these mods are successful, I would rather anyone else not *have* to add another item.

Will keep adding to this post as I go along, any comments or suggestions welcome!

Robert

Here we go again!


Indicated within .0005 over 4~5"


Barrel hole location within .001


Final drill operation, stepped up over a few sizes


.6875 reamer ready


Done


Looks good!


.1875 ream for TG holes


Numbers look familiar?


V-block threads


5/16" magazine hole @ 3 degrees


Milling the bolt shelf (about .050~.060) so the bolt will drop in easy


Enlarging the pocket on the bolt face


Fits a lot better now

Not much came out


Fits and stays great
 
See less See more
16
#28 ·
My mallory metal showed up yesterday, so as soon as I have time to get that cut and integrated into the bolt I will post pics. I hope this gets me there. Since I last had it out it will have had a new barrel, trigger, long follower, bolt mod and a heavier spring. If this doesn't do it...it may be time for a 22mag barrel:rolleyes:


Thanks again:bthumb:
 
#29 ·
Looking for Answers

Gentlemen,
It seems that many of you are doing some experimenting with the RAZOR Magnum Receiver. If you find a proven combination with parts please let me know so I can help make the build easier in the future.

Remember that spring rates will differ with barrel length, bolt friction, hammer spring and ammunition used. There are many variables. That was one of the reasons why I suggest that every rifle get tuned for the ammunition it will shoot and the parts the builder adds onto the rifle (trigger group, barrel, magazines, ammo, etc...).

If you find that the lengthened spring follower works good, I will make them up out of brass so the guys can try them in their rifles. I'll even get new springs made. However, I tested many different springs including the McMaster Carr springs you guys are trying out before settling on the existing spring. I think if you stretched the spring that came in the kit you may make up some difference with the .17 HMR round. The receiver will handle a lot of abuse but it needs a polymer bolt buffer because it is aluminum. When tuning it's important that the bolt only make light contact with the buffer if at all. The goal is to eject the spent rounds and chamber a new round with as little rearward bolt movement as possible.

Excess bolt movement will cause damaged bolt buffers and the extractor to be thrown from the bolt. The inertia of the bolt flying rearwards and striking the buffer causes the extractor plunger and spring to compress. That allows the extractor to come out the side of the bolt as there is no more pressure on its base pivot to hold it in place.

Anyway, if you guys find parts that will work and make the build easier or the rifle more reliable please let me know what they are and I will make them up or try and incorporate them into the kit.

Respectfully,

Phil Camarda
Select Fire Sales
 
#30 ·
Gentlemen,
It seems that many of you are doing some experimenting with the RAZOR Magnum Receiver. If you find a proven combination with parts please let me know so I can help make the build easier in the future.

Remember that spring rates will differ with barrel length, bolt friction, hammer spring and ammunition used. There are many variables. That was one of the reasons why I suggest that every rifle get tuned for the ammunition it will shoot and the parts the builder adds onto the rifle (trigger group, barrel, magazines, ammo, etc...).

If you find that the lengthened spring follower works good, I will make them up out of brass so the guys can try them in their rifles. I'll even get new springs made. However, I tested many different springs including the McMaster Carr springs you guys are trying out before settling on the existing spring. I think if you stretched the spring that came in the kit you may make up some difference with the .17 HMR round. The receiver will handle a lot of abuse but it needs a polymer bolt buffer because it is aluminum. When tuning it's important that the bolt only make light contact with the buffer if at all. The goal is to eject the spent rounds and chamber a new round with as little rearward bolt movement as possible.

Excess bolt movement will cause damaged bolt buffers and the extractor to be thrown from the bolt. The inertia of the bolt flying rearwards and striking the buffer causes the extractor plunger and spring to compress. That allows the extractor to come out the side of the bolt as there is no more pressure on its base pivot to hold it in place.

Anyway, if you guys find parts that will work and make the build easier or the rifle more reliable please let me know what they are and I will make them up or try and incorporate them into the kit.

Respectfully,

Phil Camarda
Select Fire Sales
These are the last two issues I'm having with mine - in .22 Mag. I suspected that I needed a heavier spring. Sounds like I'm on the right track. I also have a plunger for a Mark III coming. I'm hoping it will hold the extractor in place. But that won't solve the problem of tearing up the buffer. Hopefully, more and/or heavier main spring will do that for me.
 
#33 ·
^^Yes, I agree 100%!

I have many spring weights in hand and the ability to machine additional parts as needed...specific to my build. I am sure that everyone building a 17HMR Razor understands this difference vs the 22LR!

BTW, you misquoted me above. My reply to Guitdolin was a question, not a statement; "With 22WMR, the factory spring rate does not function correctly?" since he is building a 22WMR and the factory SF mainspring *should* function correctly. But again, each is "build dependant" I would imagine!

Robert
 
#34 ·
Just inspected my buffer after 100 rounds fired with an extra 2" of main spring added. It is scarred a little, but not entirely chewed up like it was with the factory spring alone.

I took the 2" extra spring out and replaced it with a 2.5" spring added to the factory spring. We'll see how that goes next time.

I also found burrs on the bolt that I had missed before. The slot on the back of the bolt that hits the buffer had really sharp edges, especially on the ends of the slot. I filed all of that smooth and rounded over the edges a bit. Hopefully it won't chew into the buffer so bad now.

I'm waiting on the extractor plunger I ordered from Midway before I put it back together and fire it again. I'm hoping that Mark III plunger will keep the extractor from falling out.

If the 2.5" spring doesn't prevent extractor and/or buffer problems, then I'll try the heavier spring from Robert. If that's too heavy, then I'll mix a little of the heavy spring with the factory spring until I find the right amount of cushion. And, yes, mine is a .22 WMR and the factory spring isn't enough.
 
#35 · (Edited)
Well, got to shoot the rifle today.

Good and bad.:bang:

The good:
Cycles and feeds fine. No issues. No feed failures, only a few FTE while messing with the different springs. With the heavy spring, the bolt travels too little and too quick trapping the ejected shell in the breech. Next round is in the pipe is ready to go otherwise. No failures to fire. I guess that's good.

The bad:
Every shell base is bulged. Does not matter light/heavy or short/long springs. Looks like the bolt mass is insufficient and spring will not compensate...at least with a 17HMR. Maybe possible with a 22WMR and stock SF bolt.

Also had one base blow out. Shattered the mag into 1000 pieces. Firing fine, then a hollow sounding round and pieces everywhere. Good thing I did not have my arm under the mag well. Would have been a hospital trip. Since it was not scoped, I got lucky and was shooting with two hands from behind the receiver.

On an odd note, all the cases come out bigger than the chamber! I believe that they are still under pressure until the case clears the breech at which time they stop expanding!

My conclusions:
1) Spring length nor thickness will not compensate for an autoloading, blowback 17HMR using the SF magnum bolt as is. With the heavy spring at an 8-1/4" length, it would barely cycle far enough and would trap the spent case in the breech. Case base still bulged. Lighter/shorter springs helped the cycling but not the bulging. Perhaps a 22WMR can be closer to the acceptable/safe zone with added spring.

2) Bolt mass is insufficient. Reviewing OMR's weights for different mfr's bolts, I can see why. I doubt that I can add enough (double the weight) metal mass to match those. I am going to try adding weight via a custom bolt handle...maybe with a 3/4"~even a 1" diameter grip on it. And will machine a maximum length sst follower. With a longer full size portion as stukpedal/Brian suggested. I will look into drilling out the center and adding lead as a filler.

3) Next step if the 17HMR will not function safe and reliable, buy a 22WMR barrel and try that. The 17HMR is fun to shoot, but it cannot be fired safely and consistently as it is.

Robert

Cases caught in breech due to too strong/long of a spring


All bases bulged...does not matter what weight/length spring. Fired and ejected fine. All cases numbered relative to the spring weight/length used.


Base blowout. Might not have been fully seated? Or fired OK, but got short cycled and smashed when the base blew out? Blew out exactly opposite the firing pin, so at the unsupported area of the bolt, straight down.


Look how much shorter the case is!:eek:


One shot cost $25...whats left of the mag.:mad:
 
#36 ·
It's not all bad news...just think of the cool stuff you have for your wall of shame:D

Seriously though, your case bulge problem seems strange. I didn't inspect every one of my spent cases, but I don't remember seeing any that were like that. I'm almost positive I didn't have any were the rim was ballooned, but like you said, that could have been the heavy spring causing that.

As far as mass, I don't think (here comes an opinion, not a fact) that the bolt needs to weigh as much as the factory Ruger in the S.F. setup. I think (see insert above) that if we can make decent jump in mass, say 20-30% range, that the spring will make up the difference. But I'm yet to prove that, hopefully I will get mine together this week and have some better info.
 
#37 · (Edited)
It's not all bad news...just think of the cool stuff you have for your wall of shame:D
^^Yeah, and lived to tell!:rolleyes:

I think that the heavier spring might have caused the excess bulging. A softer spring would allow the pressure to vent off sooner. Maybe lighter, up to the point of buffer carnage is preferable! I did not get a chance to try the 7" medium weight. Or 6" medium. These still have to be somewhat stronger than a stock SF spring. On a bright note, the buffer did not get mangled.

Going to try and bulk up the bolt as much as possible. Then try the springs again.:bthumb:

Keep us posted on your mallory metal insert!

Robert
 
This post has been deleted
#39 ·
A stronger spring should have "re-tarded" the bolts rearward movement and the cases would not have been bulged, because they would have remained in the chamber longer.
That is the whole idea of the spring/bolt mass. Keeping the bolt from moving too quickly.
More I think about it, the more I believe it was an OOB.

There is a double ring at the base...where the cartridge was probably not fully seated and supported. Since the thinner case material was exposed, the ignition popped it...out at the bottom exactly where the relief is on the bolt recess. Same shape and location.

On the spring issue, I did get to try 4 different weights and lengths. All of the cases were bulged. I did not try any of the lighter weights/shorter lengths. I did not get to the med weight, stock 7" length before the fubar.

I can go down to ~6" OAL and still (barely) close the bolt. I am leaning towards a lighter spring than I was using. I believe they were too stiff. My buffer looks untouched. I need to lessen the spring so it gets to the buffer sooner and harder.

I think thats what causes the base bulge...the case is supported too long and gives the base time to bulge out. If the case is retracted sooner, the pressure is relieved sooner. Just a guess.

Thanks again for your help!:bthumb:

Robert
 
#38 ·
Thanks for the info, Ted! Will keep that in mind next time out! :bthumb:

Hmm, I did not get to 5 mags full!

Hand fed and single shot the first five, checking cases and bolt closing/firing pin strikes, etc. Then did 3 mags w/only 2 rounds each to be sure they fed correctly and insure no double taps or full auto. Then loaded 2 mags w/9 rounds each to check for full mag and last round feeding. Did not get to the second full mag.

Around the 5th or 6th round of the first full mag is when the base exploded! I did not check every round for bolt correctly in battery. In hind sight, I should have. It was just feeding and firing so smooth and nice.

So only around 16 or so rounds total.:eek:

Just did a drawing for a bolt handle w/.750 full round knob and another full length follower w/extended nose. Going to drill and fill w/lead.

The quest continues!:D

Robert
 
#40 ·
Its a long @zz 20"!

It was the shortest (only) barrel I could find, and I thought I was lucky to get it. Would cutting it down or finding another that is 16~18" help? I actually prefer a shorter one, but it was available.

In your opinion, does a longer barrel need a lighter/shorter spring? Build specific, I suppose?!?

Next go round, I am going to try the lighter/shorter end of my spring spectrum.

Robert
 
#44 ·
^^ Glad it made it safely, Brian!

Hey, hows this for a 2 stage spring adapter? I machined this one today. Drilled both diameters to backfill with lead! Hole is lightly threaded so it retains the lead better!:bthumb:

I am thinking a piece of light spring about 1-1/2" long, backed by medium between 6~7" long. So many combinations!

Robert



 
#48 · (Edited)
I wanted to fill the fat end for more weight. Not sure if just the small diameter for the full length would be worthwhile.

The follower is always in contact with the tab on the bolt. I left the wall a little thicker for that reason. If it goes south, I can make another. The new follower is .7oz/22g. I am interested to see how much weight that amount of lead will add...thats for tomorrow! I'm hoping for 2~3 oz total with the handle mods.

I am looking at some mods to a stock Ruger charging handle. Need to see if it is basically the same dimensions (sans the bolt tab) as a stocker. There is room for a wider, longer bolt tab on a modded handle!:D

Shane, you're welcome! Hope it works for you! Your 22WMR is the plan "B" for me if this 17HMR is too much of a headache! Just as nice of a rifle IMO! :bthumb:

Robert
 
#51 ·
I thought it was around .052!:mad:

Threw some calipers on it when I got it just for grins, and figured that was correct for a 17HMR. Going to face that boy off.

Shane, a pair of digital calipers will do, but a depth micrometer is the preferred tool! Figures, another mod to do! G/L!:D

Once again, thanks for the info Ted!

Robert
 
This post has been deleted
#54 ·
Yeah, not something you need everyday!

Try the lines...the human eye can see differences of a couple thou...as long as there is something to compare it against. Of make/find a shim at the correct thickness and use the force...uh...fingernail to check.

At least the pocket is too deep, it would be a lot harder to deepen it on the SF bolt. Those suckers are hard!

Robert
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top