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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
RMS65
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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
rc.

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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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