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Discussion Starter #1 (Edited)
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Tried some load development for the 1st time.
I borrowed a friends shooting vise. The problem with it is it didn't have any way to lock in the traversing adjustment, and with my eyes I couldn't tell if it was staying on target consistently. Also every time I shot I would have to loosen the front clamp and push the rifle back down about an 1/8" because recoil would push it up. Now for the technical data.

LC match brass sized and trimmed to 2.05"
CCI primers
168gr SMK
IMR 4895 powder
seated to 2.8"
all charges were measured not weighed except for 2nd 40gr load which I measured and checked weight to verify that varied no more than .1-.2r.
Had about 50% that varied by .1 gr and a couple that varied. 2 gr.
Shooting crony Beta used for velocity set at 15' from muzzle.

Rifle is a Polytech standard with about 500 rds through it. Its head space is 1.638 according to Lazerus 2000 method. The barrel is over indexed so front sight is way right of center. I did add a NM FS to get rid of polytec fake.

1st load 39gr 4895
Lo 2264fps
Hi 2399fps
Avg 2307
Es 135.1
Sd 44.5
5" group

2nd load 39.gr 4895
Lo 2331
Hi 2357
Avg 2344
Es 25.89
Sd 7.54
unfortunately problems with shooting vise all shots hit off target to right

3rd load 40gr 4895
Lo 2332
Hi 2404
Avg 2372
Es 71.83
Sd 23.17
3" group this was my best of the day so I loaded up ten more to verify

7th load 40gr 4895
Lo 2380
Hi 2447
Avg 2402
Es 67.87
Sd 19.46
5-1/2" group
so 2nd round of 40gr didn't tell me if this is my sweet spot.

4th load 40.5gr 4895
Lo 2350
Hi 2428
Avg 2399
Es 78.28
Sd 23.13

5th load 41gr 4895
Lo 2394
Hi 2467
Avg 2440
Es 72.73
Sd 23.74
5" group

6th load 41.5gr 4895
Lo 2452
Hi 2509
Avg 2482
Es 56.44
Sd 17.69
3-1/2" group with 2 flyers stretching it out to 5" might have to try this load again.
I guess I have a battle rifle not a target rifle. Oh well it was still fun. I think I walked a mile yesterday just going back and forth to the target.

Pond finally went down enough so I can get around to my target's.
I tried to fix my friend's shooting vise by adding a lock bolt to the traversing adjustment. It didn't work as planned. I started the day with a scoped rifle to see how lock would work. Disappointed in that. Finally started in with more loads for M-14.
All loads used IMR 4895, 168gr SMK LC Match brass sized to 2.005 COAL 2.8
1st load
Lo 2490 fps
Hi 2527 fps
Avg 2502 fps
ES 37.44
SD 11.57
Group 5"

2nd load
Lo 2535 fps
Hi 2574 fps
Avg 2552 fps
ES 39.38
SD 12.00
Group 3"

3rd load
43 gr
Lo 2567 fps
Hi 2596 fps
Avg 2582 fps
ES 29.19
SD 10.04
Group 3"
I still used the shooting vise but instead of standing off to the side and pulling trigger I got down onto the stock like normal and adjusted the sight's each time before I shot.
42.5 and 43 gr loads started to show some flatting of primers. Gonna try again in the near future, maybe try some different powders. I felt more confident this time with my sight picture.

4,310 Posts
I bet you will do better off of sand bags or a bench rest. Others might disagree but I hate clamp on rests.

Generally with the M14/m1A 41.5 (or 1/2 tenths more) is about it.

A flattened Primer is telling you something.

1,019 Posts
I've "tuned" a Polytech I have for practice as it saves wear on the match rifle barrels. I use it in offhand, rapid sitting, and rapid prone. People at the range are very complimentary seeing the Polytech in action, then amazed when they see what a match conditioned rifle can do. I'm an average shot imo.

If you are seeing groups like this at 100 yds, it seems to me there are loose components and/or excessive headspace in your rifle for what you are shooting. For example, I push a 168 gr. HPBT with IMR 4895 or 4064 around 42 gr, same COAL. Its accurate in the Polytech and match rifles. Good enough to wear out the X-ring at 100 yds. on an SR-C target (std. target for 200 yds, but good for load development and testing).

As mentioned, try a bench with a support or off sandbags. If the groups aren't closing, then check the rear sight assembly for loose fit or slop in the rack. The overindexed barrel is going to be a challenge for sights.

1,019 Posts
Another area to review is your ammo. As a test, weigh all powder charges. This is a slow PITA procedure, but you eliminate powder quantity as a variable. Make sure you've either crimped the bullets or use a consistent neck tension. Be aware crimping should be light. And one other variable to test is the primer. CCI makes BR-2 primers. I've used those, 200 and 34. All three can give excellent results, but usually in different rifles, with different powders and various charges.
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