Gunsmithing Advice Needed

[muleman]

I had a Re-barrel Chambered, Action & Bolt trued in 30:06. I got it back & Shoots great at reduced charges(308 max Loads)I try shooting mid range loads to max loads it opens up to 1-1 1/2"?
I've tried 155, 178, & 208 Amaxs, same with all of them.

If I drop down 7-10 grs from max with any powder it shoots 3/8-1/2" groups, when I start upping the powder charge you can watch the groups open up. I've never seen this & thought I'd see what you experts say about it before I call the Smith.

 

[Hookturnr]

Re: Advice Needed

I have a very tight chambered 300RUM that runs the same way. Try running it over a chronograph and see what your velocities are and then proceed accordingly..

 

[jake6547]

Re: Advice Needed

most guns will tell you want they want to shoot not the other way around.

 

[my human host]

Re: Advice Needed

Could you give us the whole story? I'm inclined to think you have a fitting problem. Bedding, a screw that's too long, bolt handle touching the stock, etc.

 

[hero's machine]

Re: Advice Needed

What's a ladder test do?

 

[muleman]

Re: Advice Needed

I couldn't make heads or tails out of the ladders I shot, but they were from midrange to max velosities. I've checked all the torgue settings, and just been playing with it when I discovered it would shoot & Quit well at very low charges. The 155Amax with 57-57.3 grains (of RL22 no less), .015 off the lands shoots 3/8" groups. I had tried H4350, Imr 4895, Imr4064, & Varget, I then went to H4831sc with the 208s which is what I started with & droped the charge down & the 208 Amax shoots 46-47gr of H4831sc in 1/2" groups, as I try to up the powder charge the group size grows larger with every increase, by 52gr it's shooting 1 1/2". groups.
The RL22 was pure accident on the 155s as I had been trying it on the 208s. I need to go back to the 4831 or 4350 & try reduced loads with them to see the results.

I thought I'd ask here what you guys Knew as this baffles me?

Any Thoughts Appreciated!

Wayne

 

[my human host]

Re: Advice Needed

Has the rifle been bedded?

 

[muleman]

Re: Advice Needed

Yes, The Smith also bedded it. Has 26"-#5 contour Shieln Barrel, was threaded for suppressor, pretty much gone over.

Jake6547, I'm aware of each gun liking it's own recipe, but why will it only shoot at such drastically reduced loads. I'm not a speed freak but at these loads I just as well gone with .308.

 

[Greg Langelius *]

Re: Advice Needed

Just for an experiment, try working up a load with a flat based bullet. If it performs more as expected, I think you'd have some critical evidence.

Maybe the BT's get increasingly upset by asymmetric muzzle gas release as pressures go up.

If so, I'd suspect the crown.

Greg

 

[muleman]

Re: Advice Needed

Greg thanks, I will try some flat base bullets, and post the results. I shot it first with no Brake then put a Muzzle brake on it, just for the comfort. I've had it on & off a couple times but it didn't make any difference.

 

[muleman]

Re: Advice Needed

Greg, The courosity got the best of me. Winds blowing from 10:00 to 2:00 at 5-12mph, so not the best for a 150gr bullet. I used a 150SP with Imr4064 started at 45gr-shot 3/8", 47gr-shot 5/8",
49gr-shot 3/4", 51gr-shot 1/2", 53gr-shot 3/4",55gr-shot 3/8",
57gr I only shot one as I had slight Extractor marking & tighter bolt lift, Hornady 8th shows 57.6 Max. It appears there's Merit in your thoughts, as anytime I cranked up the powder charge the groups would go out to 1 1/2" before I could reach
max load. The conditions weren't the best today so I'll repeat this with anouther powder (H4831sc) when the winds die down.

I'm not familiar with your remark "Asymmeric Muzzle Gas Release as pressures go up". Wouldn't this have some effect also on a flat base bullet as well if it were a Crown issue?

Wayne

 

[Greg Langelius *]

Re: Advice Needed

If the crown is not contoured evenly all around (or is not symmetric), venting gas will blow past the BT unevenly as it emerges, tipping the bullet, creating instability that can open up groups. As pressures increase when charges are increased, this tipping may become more pronounced.

If the crown is contoured properly, the gas vents evenly, and tipping is not an issue.

With the FB bullet, the base clears the crown much more quickly, giving the gas less opportunity to tip the bullet. The BT acts like a sail to catch the unevenly venting gas at a nearly right angle. The BT has no such sail area, so little or no tipping can occur.

Greg