Unusual component interactions in 260 loadings.

[wchartz]

I got a new bolt action tactical build and started my load development. The barrel is a Kreiger standard Palma 1:8.5 and chambered with what is called a Lapua reamer. I used H4831SC, H4350 and H414. The bullets were SMK 142 and 123. Hornady 140 A Max and Berger 140 VLDs.Primers are 210Ms. Brass is Lapua. I did all of my testing at 100 yds. off of a bench in very good conditions. All groups are five shot.I could not find any combination that would give me groups consistantly under .75" I had a lot of tight three and four shot clusters but seldom got a full group under .5". I changed all the usual suspects, Scope, mounts,action screws, seating depths. Checked bullet runout, .0013" maximum. I called my gunsmith for help and said he would check it out if would send it back but he first asked me to call another of his customers that he had built a similar rifle for and see what he had to say. I did and found out that the other customer had the same make and spec barrel cut with the same pattern reamer. I described my symptoms to him and he said that his rifle had acted the same way. His would only shoot well with Lapua 139s. I got a box and eureka, I found it. After determining that the gun preferred to shoot with the bullets backed off of the lands my four group aggregate was .26". It shot good with the bullets jammed .010" but better backed off. I have a few hundred new 7mm-08 Winchester brass that I ran through a Redding FL 260 die. I tried those in place of the Lapua brass. The cases had the flash holes reamed and the mouths chamfered. The primer pockets seemed uniform and the primers seated well by feel and the primers were flush to -.003" low. The neck tension is quite high on the Winchester brass. I initially increased the powder charge by .2 gr. since the Winchester brass has more capacity. I ended up increasing the charge by a total of .5 gr.
This got me within 5 fps of my velocity using the Lapua brass. My next four group aggregate was 1.18" with nothing less that .90" I am well pleased that the rifle will shoot right at a quarter minute with any combination of components. However the extreme differences in group size due to different match bullets and brass is a little disconcerting. I have read the other post on this thread where one poster commented that his Winchester brass would not shoot until he turned the necks and annealed the brass. The neck thickness on my Winchester brass runs .013-.015. The Lapua runs .014-.015. My chamber neck diameter is .298. That neck variation should not cause a four fold increase in group size. The neck tension might but I will have to do some anealing to verify that. It still seems like a stretch to have that condition cause such a decrease in accuracy.
By the way the rifle was built by Jon Beanland. He builds a fine rifle and I have never experienced any better customer service but I have and am experiencing much worst customer service from some nationally know gunsmiths as well as just plain shoddy work.

 

[jrob300]

Re: Unusual component interactions in 260 loadings.

I believe you were referring to my post.

A couple other thoughts...

Is the Winchester brass virgin? Lapua brass fit my chamber nicely and shot well from the start. Winchester brass is much smaller in OD (fits loosely in the chamber when new) and shoots better after fire forming. I get poor accuracy with virgin Win. brass in my rifle.

How much neck tension do you run? I use a .294 bushing on my Lapua and a .290 on my turned (to .013) Win. I may move up to a .291. Too much or uneven neck tension will definitely cause change in POI.

John

 

[Fuzzball]

Re: Unusual component interactions in 260 loadings.

"<span style="font-style: italic">His would only shoot well with Lapua 139s. I got a box and eureka, I found it. After determining that the gun preferred to shoot with the bullets backed off of the lands my four group </span>"

Goodness, a rifle that shoots best with a well selected bullet, and OFF THE LANDS TOO! Who would have suspected?

 

[wchartz]

Re: Unusual component interactions in 260 loadings.

My point was not that a certain bullet worked better than another but that the degree of difference between good VLD bullets was suprising. As to seating depth I noted that jammed or jump did not make a big difference. I have never found that it does make a big difference.
My brass is new. I use a .292 bushing for the Lapua. A .393 does not give enough tension.

 

[wchartz]

Re: Unusual component interactions in 260 loadings.

I do not want to fire form my brass with bullets. I would like to try fire forming with a light charge of powder and a filler. Does anyone have a good load for this?

 

[shootist2004]

Re: Unusual component interactions in 260 loadings.

I hear people use pistol powder and creme of wheat but Ive never tried it. seems messy.....

 

[2clicks]

Re: Unusual component interactions in 260 loadings.

Another supposed quirk of the 260 is that after about 200 rounds things settle down with it. I too have had some hassle with settling on a load for my GAP 260, I think mostly because of the 4 excellent bullet choices, Hornady, Berger, Lapua, Sierra.

I should have just picked one bullet and made it work the way I did with my .308's.

As it is now 43-43.5grs of H4350 in 7mm-08 Winchester (necked down) or RP 260 brass works well. With a 140 class bullet. My loads are about .015 thou off the lands.

I hear the Lapua brass was supposed to be thicker on the necks causing some chambering issues on chambers reamed for the thinner American brass. I don't know if that's an issue any more but Gap's match 260 reamer was designed for the thinner USA made brass so I never tried any Lapua brass...

Dam good shooting rifle though I'm glad I got it !!!

 

[Paladin2147]

Re: Unusual component interactions in 260 loadings.

I fire form 6xc brass from 22-250. The 22-250 case after coming out of the 6xc sizer looks like a malformed mushroom. I use a full charge to fire form. The shots during fire forming are not noticeable less accurate than the fully formed brass. I do not think that going to a light "filler" load is either safe or effective. But if you think that will solve your problem with a rifle that shoots 1/4 inch - have at it.

 

[wchartz]

Re: Unusual component interactions in 260 loadings.

I would not mind fire forming with full charge loads if the loads were reasonably accurate. Right now the Win brass is terribly inaccurate. I plan on taking 50 of them and turning the necks and annealing them. If that makes them accurate I will do the rest.

 

[Greg Langelius *]

Re: Unusual component interactions in 260 loadings.

Bullet preference is probably more closely related to the chamber/lands leade angle. This something that can be influenced by a particular throating reamer.

I found that the 139 is a good bullet, but for some reason, can generate peaky pressures. This may be related to leade angle and jamming.

My barrels are L-W Savage prefits with their SAAMI chamber. My loads use R-P brass, 142SMK's, and right around 44gr of H4350. They seem to work better when they jump. I'm estimating my velocities at around 2850fps from a 28" 1:8" barrel, based on observed drop.

I do my fireforming during preliminary load development, otherwise, I start my brass out with a F/L resize and skip the fireforming step. Often those 'fireforming' loads will be the best grouping loading cycle in that brass batch's lifespan.

I don't fireform per se. It wastes a loading cycle, and adds to bore life degradation. Putting anything down a barrel besides a 'for-real load' bullet makes me cringe. Cream of wheat? OK; but for breakfast, before the trip to the range.

Greg

 

[Greg Langelius *]

Re: Unusual component interactions in 260 loadings.

I've been working at precision shooting and handloading for about the past two decades, and have become mildly skeptical of many of the more complex techniques many handloaders employ.

It it simplest, I think that simply assembling the ammo, with due diligence to consistency and detail, will produce ammuntion that has better performance consistency than the broad majority of shooters can fully utilize.

While I know there are a signficant number of shooters out there who can make full use of the advantages the more esoteric techniques can provisde, I am equally convinced that for most of it, indulging such techniques is little more than an exercise in conceit.

For example, this w/e I shot a ten round group at 250yd that was just about at 1/2MOA, using an AR. It employed Serbian (PPU Headstamp) brass, reclaimed (collet pulled) 50gr Nosler BT's, CCI 200 standard primers, and 26.5gr of W748, simply drop fed from a Dillon Powder measure being employed in basic progessive mode, no weight checking being employed. The dies were RCBS 2-die F/L, screwed down to touch the RL550B's baseplate. The OAL was .015" short of SAAMI Max, at 2.235".

I make no claims to this being an intentional outcome. I was simply flabberagasted by the result. I was simply doing a feeding/function test of an arbitrary book-quoted load in a new rifle. Yes, it's only one group, but it's also ten rounds. I have a fair confidence that it could be repoduced at will under reasonably favorable conditions. I just assembled another 110 rounds of this load, the same way, to see if it provides consistency. The testing will be done under match conditions.

But no denying, there was also no effort to 'match prepare' that ammo. If luck wasn't involved, luck does not exist. Still, it sorta puts the question to extreme handloading measures, too.

Greg

 

[Paladin2147]

Re: Unusual component interactions in 260 loadings.

Greg, I cannot agree more. Some loads just shoot, others will all the bells and whistles still suck. With the short bbl life with some ctgs.. every round counts.