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Old 08-21-2019, 08:16 PM
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Inconsistent POI with 17 HMR



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I wanted to reset my scope in the rings for my Ruger American 17 hmr. I haven't cleaned the gun in over 100 rounds. I had been shooting with the CCI 17 grain Vmax. I wanted to see how closely the Hornady 17 grain Vmax would correspond to the same point of aim as the CCI rounds. After first adjusting my reset scope for the CCI rounds I tried the Hornady ammo. The result was totally unexpected. With the 17 mach 2, I found it pretty much didn't matter what ammo I put in the gun as long as it was the 17 grain vmax, point of impact didn't change much. I was expecting similar results with 17hmr. What happened was totally unexpected. There was about a two inch shift to the right with the Hornady ammo compared with the CCI. I then adjusted the scope for the Hornady ammo and switched back to the CCI. It shot as you might expect to the left considerably. I've got to scrub the bore and shoot it again to see if it still behaves this way. Groups were not as consistent as I had hoped with a bit of vertical string. CCI rounds had a length of about 1.355 to 1.365 inch long and Hornady 1.345 to 1.352 inch. Has anyone noticed a difference in average ammo length and dramatic changes in point of aim for the 17 hmr?
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Old 08-21-2019, 10:47 PM
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Welcome to 17hmr. Yes that's very possible. There's usually large POI shifts between different bullet types. Polymer tips vs hollow points vs fmj vs game points. Even with the same bullet types (which almost all are cased by cci) POI shifting is common just with different lots of ammo. Seems higher quality guns get less shift but there's always some.
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Old 08-22-2019, 10:20 AM
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I have also seen the POI shift among different lots of .17HMR and .17HM2. I have been measuring bullet seating depth (as measured from the ogive to rim) and sorting into groups for testing. In my rifles, it seems as though bullets seated closest to the rifling (longest OAL) give the most consistent groups, by eliminating the fliers. I am still testing, so too soon to draw conclusions, but the results have been positive. I recall that Steven Boelter ( of RRDVegas) had improved accuracy of .17HM2 by measuring and sorting bullet seating depth from the ogive. Handloaders would understand this principle as the seating depth affects chamber pressure and velocity.
It would be interesting if anyone else has done similar testing and post results here.
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Old 08-22-2019, 11:06 AM
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joet, thanks for posting. I was just doing a quick and dirty OAL test with my caliper. I have no way to measure to the orgive on a 17hmr but I understand what you are talking about. I've reloaded a bit. I wasn't sure if maybe the change in impact point was due to different powder lots or different overall length. I appreciate you confirming my suspicion about length having a significant affect on point of impact. I haven't sorted Mach 2 or HMR ammo but what you say makes sense. Obviously the closer to the lands the better. rc
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Old 08-22-2019, 02:15 PM
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Quote:
Originally Posted by joet333 View Post
I have also seen the POI shift among different lots of .17HMR
Likewise.
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Old 08-30-2019, 02:32 PM
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I shot some Hornady 17 gr. V-Max before I switched over the A-17. I don't know if the extra 100 '/sec made all the difference or not, but the A-17 was about 2 inches higher at 100 yd.s.

I didn't shoot any after setting my scope for the A-17. I was running out of time and wanted to check out my Mdl Five.

It will probably be a couple weeks before I have a chance to shoot the 17HMR again. I will shoot both. in fact, I have some of the Cu .17HMR that I am going to shoot just to get rid of the 1/3rd box I have left.


VH
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Old 09-18-2019, 06:51 PM
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I have been looking back at this tread for some time, obviously almost half a month.

I have a question and a comment. Question first:

Where can one find the OAL chamber dimension with which to check the cartridge length ?

Comment second:

Having been cognizant of the lack of "match grade" ammo for this round I sampled several different loads and once I found a good one I went back to the supplier with lot number in hand and purchased a bunch just as I do with my 22's. It just made sense to me to do that as it would seem to reduce the fluctuations in impact on target at least to some degree.

Given the lack of said Match Grade ammo one can only hope for the best and when found it behooves us to stock up on said ammo.

A little late to the party but...… JMHO
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Old 09-19-2019, 10:38 AM
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Quote:
Originally Posted by huntschool View Post
I have been looking back at this tread for some time, obviously almost half a month.

I have a question and a comment. Question first:

Where can one find the OAL chamber dimension with which to check the cartridge length ?

These dimensions are stated in SAAMI Specs., page 9 for .17M2, page 10 for .17HMR.
https://saami.org/wp-content/uploads...2018-06-13.pdf


Comment second:

Having been cognizant of the lack of "match grade" ammo for this round I sampled several different loads and once I found a good one I went back to the supplier with lot number in hand and purchased a bunch just as I do with my 22's. It just made sense to me to do that as it would seem to reduce the fluctuations in impact on target at least to some degree.

Given the lack of said Match Grade ammo one can only hope for the best and when found it behooves us to stock up on said ammo.

A little late to the party but...… JMHO
I modified my rimfire gauge to measure the ogive length from the base of the rim, and sorted several lots of Eley, Hornady, and CCI (.17M2) into consistent groups.
I found that for my Kimber K17 ProVarmint there was a certain ogive length that gave consistently smaller groups with no fliers. Within any given lot the ogive length could vary by as much as .016" due to seating depth. This is considerable and points to the lack of quality control in these rounds. Hence no "match grade" ammo is available for .17M2 (and probably for .17HMR) simply due to variations in bullet seating depth, as well as other factors. One cannot measure the OAL with any meaningful results because the little plastic V-tip dimensions can vary by .010".
In my testing, the best sorted ammo lots made 5-shot groups at 50 yards as small as .377" while the same lot with different ogive lengths shot as poorly as 1.301".

I don't claim that sorting can make match grade ammo, but it did eliminate the fliers, at least for my rifle. Other rifle chambers may not be as sensitive as mine to variations in ogive length.

It would be nice if CCI would step up to improve quality control, but I doubt that they would view that as cost effective.

I know others have stated that sorting rimfire ammo is a waste of time, and I have found that to be true of .22LR. However the .17M2 and .17HMR have copper jacketed bullets that seem to behave similar to centerfire rounds with respect to chamber pressure.
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Old 09-19-2019, 01:21 PM
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Quote:
Originally Posted by joet333 View Post
I modified my rimfire gauge to measure the ogive length from the base of the rim, and sorted several lots of Eley, Hornady, and CCI (.17M2) into consistent groups.
I found that for my Kimber K17 ProVarmint there was a certain ogive length that gave consistently smaller groups with no fliers. Within any given lot the ogive length could vary by as much as .016" due to seating depth. This is considerable and points to the lack of quality control in these rounds. Hence no "match grade" ammo is available for .17M2 (and probably for .17HMR) simply due to variations in bullet seating depth, as well as other factors. One cannot measure the OAL with any meaningful results because the little plastic V-tip dimensions can vary by .010".
In my testing, the best sorted ammo lots made 5-shot groups at 50 yards as small as .377" while the same lot with different ogive lengths shot as poorly as 1.301".

I don't claim that sorting can make match grade ammo, but it did eliminate the fliers, at least for my rifle. Other rifle chambers may not be as sensitive as mine to variations in ogive length.
joet333:

Thanks for the link. I dont know why I did not think of that. Old brain I guess.

So, to make the "short" of it (no pun intended) if one could only measure and sort by OAL the longer cartridges may well prove to be the better performing loads. Would that be a very simple analogy to your testing ? Knowing that there are surely some other factors at play.

Thanks
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Old 09-19-2019, 02:27 PM
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My testing showed that measuring OAL (total cartridge length) was misleading because of the gross variation in the dimension of the plastic tip length. That fact is what guided Steve Boelter to measure the length from the ogive to the base of the rim. That dimension will be a more accurate measurement, and he believed the ogive has more effect on chamber pressure. I just followed his recommendation.
Measuring a box of 50 will give lots that cover a range of .010-.016" variation in ogive length, with a normal bell-shaped distribution. For my rifle, best groups came with ogive lengths that were middle of the pack. Increasing upwards from the optimum length, as the bullets became seated closer to the rifling I saw some extreme fliers. Measuring a box of 50 takes about 15 minutes once you have the rimfire gauge set up to measure the ogive. I tried the quick-and-dirty method of measuring OAL with calipers, but that was disappointing due to the plastic tip variations that I mentioned above.
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Old 09-19-2019, 05:59 PM
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Quote:
Originally Posted by joet333 View Post
My testing showed that measuring OAL (total cartridge length) was misleading because of the gross variation in the dimension of the plastic tip length. That fact is what guided Steve Boelter to measure the length from the ogive to the base of the rim. That dimension will be a more accurate measurement, and he believed the ogive has more effect on chamber pressure. I just followed his recommendation.
Measuring a box of 50 will give lots that cover a range of .010-.016" variation in ogive length, with a normal bell-shaped distribution. For my rifle, best groups came with ogive lengths that were middle of the pack. Increasing upwards from the optimum length, as the bullets became seated closer to the rifling I saw some extreme fliers. Measuring a box of 50 takes about 15 minutes once you have the rimfire gauge set up to measure the ogive. I tried the quick-and-dirty method of measuring OAL with calipers, but that was disappointing due to the plastic tip variations that I mentioned above.
joet333:

Thank you for the reply.

I wonder, since I would be measuring 17 HMR rounds with no "plastic" tips if there would be a difference. Your thoughts.....
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Old 09-19-2019, 06:22 PM
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That may be worth a try...the solid copper jacketed or HP tip may be more consistent than the plastic tips. Let us know how it works out. I'll be interested to see your results.
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Old 09-19-2019, 07:52 PM
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Quote:
Originally Posted by joet333 View Post
That may be worth a try...the solid copper jacketed or HP tip may be more consistent than the plastic tips. Let us know how it works out. I'll be interested to see your results.
joet333:

I will. It will be a bit as I have a kind of full schedule for the next few weeks. Retirement is not a slow time.... LOL
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Old 09-20-2019, 10:07 AM
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I did a similar comparison between CCI and Hornady with the 17VMax a while ago. I found the point of impact at 50 yards to be about 1/4". I was using a CZ455 at the time. The other thing I was thinking when I first read the OP's post was cleaning. I was wondering when was the last time the barrel had a deep clean with copper solvent. I usually clean around after the range with solvent. Every once in a while I'll really go to town and do a slow deep clean with solvent vs my usual quicker clean with solvent.


Last edited by Gmww; 09-20-2019 at 11:11 AM.
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