17 HMR Torque Test Advice Needed

[222Jim]

I'm looking for advice on designing an action screw torque test for my Cooper 57M in 17 HMR.

I'm happy with it's overall performance, but I'm wondering if I can turn longer range "Hail Mary" ground squirrel shots into something with more certainty through the action screw torque (they might be pests, but deserve a quick death nevertheless).

The torque right now is set at Cooper's recommended 35 in-lbs for the front and 25 in-lbs for the rear screws. Groups are typically:

• 0.35 - 0.50 MOA mean radius with 17 gr polymer tipped ammunition, and​
• 0.55 - 0.65 MOA mean radius with 20 gr hollow point ammunition.​

These results are all based on 20 shot groups (shot as 4 5-shot groups) @ 100 meters and analyzed using the OnTarget TDS program.

Before I start monkeying around with the torque I'd like to learn from you on designing a test, i.e. minimum and maximum torques, test increments, same or different front and rear torque?

Thanks in advance.

 

[TRSR8]

I'm looking for advice on designing an action screw torque test for my Cooper 57M in 17 HMR.

I'm happy with it's overall performance, but I'm wondering if I can turn longer range "Hail Mary" ground squirrel shots into something with more certainty through the action screw torque (they might be pests, but deserve a quick death nevertheless).

The torque right now is set at Cooper's recommended 35 in-lbs for the front and 25 in-lbs for the rear screws. Groups are typically:

• 0.35 - 0.50 MOA mean radius with 17 gr polymer tipped ammunition, and​
• 0.55 - 0.65 MOA mean radius with 20 gr hollow point ammunition.​

These results are all based on 20 shot groups (shot as 4 5-shot groups) @ 100 meters and analyzed using the OnTarget TDS program.

Before I start monkeying around with the torque I'd like to learn from you on designing a test, i.e. minimum and maximum torques, test increments, same or different front and rear torque?

Thanks in advance.

If properly bedded, you’re wasting your time.
With no pillars use 25-30 in lbs and call it done,

 

[222Jim]

If properly bedded, you’re wasting your time.
With no pillars use 25-30 in lbs and call it done,

Why? I started off being skeptical action screw torque would have any affect on precision, but there's to much information, albeit mostly anecdotal and/or not statistically significant, that action screw torque has an affect on precision for me to ignore without pursuing this further.

Thanks.

 

[Clancy]

I would have it pillar bedded regardless.

After that, torque isn’t of much importance.

 

[jpx2rk]

Something else to remember/consider is that 17HMR ammo is about as consistent as 22lr ammo is, one lot shoots great like you posted above, and the next lot, not so much. Using your current ammo that appears to be very consistent for testing would not be beneficial IMO, buy some other lots of ammo and see how it shoots, maybe do testing with it, then try the good stuff.

 

[doclu60]

If the rifle is pillared and bedded, torque settings are not going to do much, if anything.....refer to post #2. That post is correct. If the stock is NOT pillared and bedded, use the recommended torque values from Cooper and look at ammo, or have the rifle pillared and bedded and STILL look at ammo.

I have a .17HMR (CZ 457 Varmint) and I did work on better accuracy for it. First thing was action screw torque, no happiness. Second thing was I got rid of the POS Boyd's At-One stock and replaced it with a factory CZ Varmint stock that has the plastic pillars. Forgot what I torqued them at but think it was 35"lbs front and rear. Some happiness. Now, the best thing anyone can do to increase accuracy with a .17HMR is to length sort the ammo. Doesn't have to be the 'purist approach' of length to ogive, just a simple OAL length of the cartridge from base to bullet tip. I noticed some of the cartridges were different lengths, just by an eyeball on them, when they were sitting on the bench during weight sorting (weight sorting, don't do it, waste of time) so I got the calipers out and checked a few. Oh my, radical differences! So, I sorted by OAL and tested. If you do this, it will change groups. It also has the benefit of finding the exact length your specific barrel likes. All the sorted ammo will pretty much shoot better when segregated into length groups, but you will find certain lengths that shoot really good. Those are the lengths your rifle really likes. QC on these, like some other factory RF ammo, is poor at best. And as far as changing to the 'good stuff' as mentioned in post #5, there is no good stuff. Only a couple of MFG's load .17HMR, despite what brand is put on the box.

Hope this helps.............Scott

 

[grauhanen]

Why? I started off being skeptical action screw torque would have any affect on precision, but there's to much information, albeit mostly anecdotal and/or not statistically significant, that action screw torque has an affect on precision for me to ignore without pursuing this further.

Thanks.

There's an absence of reliable testing evidence that torque variations other than about 25 - 30 inch pounds for a wood stock make a difference in ammo performance on target. TRSR8's advice is sound.

Why? Rimfire ammo like .17HMR often doesn't produce reliably consistent results on target. A lot of .22LR ammo is the same. The result is that it's not possible to know if changes on target are due to ammo or torque changes.

 

[222Jim]

There's an absence of reliable testing evidence that torque variations other than about 25 - 30 inch pounds for a wood stock make a difference in ammo performance on target. TRSR8's advice is sound.

Why? Rimfire ammo like .17HMR often doesn't produce reliably consistent results on target. A lot of .22LR ammo is the same. The result is that it's not possible to know if changes on target are due to ammo or torque changes.

Thanks........confirming my belief that whatever information on screw torque vs. precision is available, it's anecdotal at best and/or not statistically valid. I'm open to changing my view if someone can point me in the direction of a statistically valid test or study that shows a relationship. But to date I've not found one.

 

[CharlieNC]

Before taking further investment, remove the action screws. Gently "rock" the action to feel if it has a consistent fit or if it teeter totters at a point. Remove the action and inspect carefully for witness marks where the wood is standing proud, if so remove wood at that location to remedy. I was going to bed a CZ when this corrected the problem.

 

[TRSR8]

Thanks........confirming my belief that whatever information on screw torque vs. precision is available, it's anecdotal at best and/or not statistically valid. I'm open to changing my view if someone can point me in the direction of a statistically valid test or study that shows a relationship. But to date I've not found one.

Most of what you read is BS internet stuff overlooking the fact that it’s more likely better conditions vs anything else.
Also, Coopers, of which I’ve owned several….the bedding is often less than stellar. Another issue, take bolt apart, 57 firing pins tend to be rough as a cobb. Clean bolt, polish pin.
Properly bed the gun, pillars would be helpful, but ultimately, with an HMR you’re ultimately at the mercy of ammo with shit quality control so regardless of gun improvements that’s always there.