OCW with an M1A?

[Grump]

Should I run the OCW test at 200 yards instead of 100? Any insights into OCW with this gas gun?

Here's why I ask:

Got some more bullets to test, trying to tweak things into a reliably sub-MOA load or two.

Past OCW tests have been mixed. One was mucked by a loose scope mount. One before that was mucked by the Trashco scope's eyepiece being loose and shifting the reticle (that's gone now).

The odd thing is that every load tested (including the last two fairly reliable tests) show LOWER bullet impacts at 100 yards as the charge weight goes up. I'm thinking this might have something to do with the weight distribution above the boreline and the 2.5 inches between the boreline and the scope's center.

The worst loads are running 2 MOA, so I'm sure the group centers can still be located well enough. Heck, I'll even run them though that target freeware I have somewhere on this hard drive...

 

[jdel]

Re: OCW with an M1A?

You might want to take a look at Practical Riflery forum. Dan's the man when it comes to the OCW.

 

[Top Cat]

Re: OCW with an M1A?

If you are looking for consistent sub moa performance from an M1-A, the rifle has to be tuned up a bit. In a standard rifle, the OCW benefit will be lost in the noise somewhat.

The big 3 are properly bedding the receiver and reinforcing the stock, unitizing the gas cylinder and reaming the flash hider. The scope mount also has to be a reliable unit like the Smith Enterprise or Sadlak and properly mated to the receiver, and the scope needs to hold zero.

The M1-A won't be able to be loaded to reach the higher nodes, but the midrange nodes will be fine. The best load will be close to Fed GM Match velocity wise in the selected bullet weight.

TC

 

[Greg Langelius *]

Re: OCW with an M1A?

If the rifle shot 1/2MOA or better, I'd go to 200yd, as the baseline dispersion at 100yd could be too small to clearly determine load preferences; but my own personal view is that the M1A probably won't shot that tight, and going to 200yd can introduce wind-induced dispersions which can cloud the issues further. This is a very basic issue that affects most instances of load testing, and some more so than with the M1A. This is why increment testing should be done with at least 3-five round groups per increment. Anything less is just not going to be reliably representative, and even this approach is only marginally effective from a statistical aspect.

Actually, I don't ladder test groups any more. Instead I have targets I make up with vertical rows of five each 1/2" yellow dots with bold black borders, and shoot one shot at each dot, five per row, three rows per increment. This way, I can see more clearly how each shot actually performs; sequentially, with reference to fouling state, and make notes about calls and wind states for each shot on another target I keep back at the bench for notational purposes. The individual targets can be arrayed side by side, or stacked atop each other over a strong light source for more objective comparison. This is one instance where thinner, more translucent target paper can be preferable.

To allow a better target presentation, I use a backing paper. It's packing paper, news print actually, from WallyWorld's packaging/stationery department, packaged about 240-250 sheets, 24"x24", for about a ten-spot.

Greg

 

[Grump]

Re: OCW with an M1A?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Top Cat</div><div class="ubbcode-body">If you are looking for consistent sub moa performance from an M1-A, the rifle has to be tuned up a bit. In a standard rifle, the OCW benefit will be lost in the noise somewhat.

The big 3 are properly bedding the receiver and reinforcing the stock, unitizing the gas cylinder and reaming the flash hider. The scope mount also has to be a reliable unit like the Smith Enterprise or Sadlak and properly mated to the receiver, and the scope needs to hold zero.

The M1-A won't be able to be loaded to reach the higher nodes, but the midrange nodes will be fine. The best load will be close to Fed GM Match velocity wise in the selected bullet weight.

TC </div></div>

Rifle is tuned, gas cylinder shimmed, bedded tighter than a nickel in a Scotchman's mitts, FS reamed, and it has a new match barrel.

Trigger's good at NM specs, too.

Scope and mount have proven reliable.

FGMM comes in 155s? Not in the original data, I know, but I'm testing 155s (again) and 175s next.

I'm mainly curious about the downward trend in group impact as velocities go from the 2700s into the 2800s with the 155s in previous testing.

 

[okiefired]

Re: OCW with an M1A?

You've already answered your question. With the high mount on your scope, I think as velosity goes up and trajectory flattens, bullet impact will drop at that distance.

okie