Help with accuracy

D.Camilleri

Well-Known Member
Joined
Jun 1, 2004
Messages
925
Location
Worland, Wyoming
Rifle in question is a custom 338 RUM, Broughton 5C 9.3 twist, 27 inches, blue printed action, jewel trigger set to 1 lb,old style firing pin and shroud, sako extractor, bell and carlson alaskan stock with full length pillar bedding, muzzle brake. Gun was built by Cloud Peak Gun Works in Wyoming and he did a great job. I have approximately 500 rounds down the barrel.

This is really bugging me. Got up in the middle of the night and pulled the action from the stock. About a month ago I bedded the recoil lug with devcon and also bedded the first two inches of the barrel in an effort to see if it would change my cold bore poi. I looked at the mounting, made sure the magazine box was not in a bind, retorqued the action screws and checked to make sure the barrel is free floated. All last year, I would shoot to distance of 700+ yards and before I left the range I would dial back to 100 to verify my zero. I would leave with a bullseye and upon returning on a different day the first shot or two would hit about 1 moa high. I started with a cold bore shot to 700 and would hit 7+ inches high. I would back off to 100 yards and sure enough, 1 inch high at 100. I would readjust my zero and then after warming the barrel up the group would mover an inch lower. I killed a great mule deer last year at just under 500 yards and the shot hit about 5 inches higher than my aim point. I finally sent my Sightron SIII back to Sightron who gave it a clean bill of health. I am waiting for the scope to show back up and right now I have a 6.5-20 VXIII that I stole off of my 300 rum.

I have read about making notes about where your cold bore shot hits. It seems that after I deep cleaned my barrel that it now needs more fouling shots to settle in. I put about 16 shots down the tube yesterday and put the gun away dirty. The groups were getting better with the more shots down the tube, but did it have anything to do with the barrel temp rising to a stable level?

All last year the poi change was 1 moa. Now that I have deep cleaned the barrel, my first shots yesterday were over 5 inches high for at least the first 4 shots on a clean bore. I dialed my turret down 3 moa and hit several shots an inch above the bullseye. As I continued shooting my group continued to drop until finally settling around 1.5 inches low. The funny thing is that my go to Berger 300 grain load was shooting a pattern and my new load of 101 grs of rl33 was grouping fairly well.

So the big question is do I keep shooting without cleaning and see how my groups go or is there something else that I should try. I have thought about seating my bullets out longer and seeing if there is a difference. When I looked at my bore through the bore scope, the throat seemed to look good and I didn't see any eroded rifling, but then I am not an expert at looking at that.

I have taken every precaution on my handloads and they are as good as I know how to make them. My standard deviation with the rl33 loads were very low at around 8 though my magneto speed.

Is there anything else mechanical that I should look at?
 
When I cleaned thoroughly last week, I removed copper and carbon. I shot some groups and removed both again. I shot today with a dirty bore and it didn't shoot very well. First six shots hit 1 inch high of the bull. The next four shots hit about 1.5 inches low of the bull. I shot my 300 gr bergers, 300 gr accubonds and 4 shot of factory federal 225 accubonds. This gun never used to like those factory loads very well, but today they shot close to one inch. They are advertised at 3020 but my magneto speed clocked them at 3200.

I went ahead and only cleaned carbon after shooting this morning. I want to see what effect this has on my other loads.

When I got this barrel new, it was recommended by my smith to just patch it with wipeout and use a nylon brush. I did this and ended up with a severly carbon fouled bore. I am scratching my head right now because this barrel has never liked loads that were set close to SAMI specs and today my factory loads shot better than any of my handloads. Yesterday when I was shooting with a very clean bore, two shot groups were not bad, but the elevation kept moving down with each two shot group until it stabilized at about 1.5 inches below the bull. I overlaid today's targets over yesterdays and many of the hits overlay each other.
 
How many firings on the brass? Annealing them? What's your sizing and seating process? What rings and bases are you using?
 
My brass is mixed up. I had a batch of 100 new cases last year. I haven't annealed any of my necks. LRT307 gave me a good clue this afternoon, maybe I am not bumping my shoulders back enough. I have set my dies to firmly contact my shell holder, but maybe it isn't enough. LRT307 told me he had a smith trim the bottom of his die so he could get the needed shoulder bump. Could this be part of the problem? Thinking back, when I use new brass, my handloads are much more accurate. I thought I did a very good job of prepping my brass as I removed all carbon, tumbled, trimmed etc. So why does bumping the shoulder back make such a difference?
 
Get yourself the hornady headspace kit and measure your brass. Then set up the die to bump the shoulder 001-002.
A buddy had to remove some material from his RUM dies also to get the correct bump. They were RCBS.
 
Well, I think I am a little closer to a solution. This morning I stopped by Cloud Peak Gunworks and visited with Trevor. He scoped my bore, worse than I thought, a lot of wear, too much to do a set back, but not terminal yet. I told him to find be a new barrel. He also checked my stock and found something very simple that I purely didn't see. The lever on my trigger that releases the bolt lock was hitting the side of the bottom metal trigger guard. I looked for something like that and still didn't see it. I need to tweak my bedding job a little to correct this issue. I will try and get that done tomorrow and see if my groups come back. As for my poi change, I have been fighting this for several years and I think it is from the barrel.
 
I wouldn't tweak your bedding job. I would use a file and remove a little material from the inside trigger cutout of your bottom metal. Simple fix. I've had to do it a few times especially when installing an aftermarket trigger.
 
I filed a little bit of material from the inside of the trigger guard and installed two small washers between the bottom metal and the bedding posts to make some clearance for the magazine box. Time to go shoot and see if there is some improvement. I also relieved the sides of the bedding where the recoil lug is.
 
About 18 years ago I bought a new old stock 308 cal parker hale match barrel, and it did a similar thing ,it was a real hummer for accuracy and almost every service match that I used it in I won, till I shot it out.(a sad Day) when I first fitted it I noticed that if the barrel was cleaned with sweets 7.62 or hoppies No9 it didn't matter, the first shot always shot 2moa low but all shots after it were bang in the bull unless I stuffed up, I left the barrel for a week uncleaned(as a one off experiment) and it didn't drop the first shot, so it liked the fouling!!!!!
when I bed all my rifles I do not extend the bedding compound more that a 1/4 of an inch beyond where the barrel screws into the receiver as I have found that you get POI changes as the barrel heats up, and have had people bring me rifles to rebarrel and bed that didn't shoot or had the problems that you are talking about on the thread.
I would go back and remove the excess bedding under the barrel and try it out again
 
Thanks, I keep this in mind. I did remove some of the bedding compound that I put on the first part of the barrel. There is about 1 1/2 inches of bedding on the first part of the barrel, but it is full size with no taper for over 2 1/2 inches.
 
New barrel is on order, Barlein #4 10 twist that will finish at 26+. My stock isn't wide enough to handle a bigger contour barrel and I really don't want the extra weight. I had also found a factory take off 338 rum on ebay with a couple of marks from removal, it is an XCRII barrel that is black, but that contour is lighter than my current barrel and it would look funny in my stock. The gun needs to shoot good and look good too. My smith couldn't find any 338 barrels in stock at his wholesalers, but I found one at Grizzly and got it coming. It should be here Tues.

I put washers under my bottom metal to create a gap to relieve the pressure from the magazine box, but it still feels tight, could it be because the magazine box for an ultra mag has a crease on the side metal to create more clearance? Is this a critical thing?
 
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