Swipe marks w/ low powder loads, 260 Rem. What's going on?

[tojan19]

So I'm trying to work up the load for the 260 Rem I had built in the LRI group buy. Brand new Lapua brass, H4350, CCI BR primers, 142gr SMKs 0.025 of the lands. The Hodgdon website has the load listed as 41.5 to 44.5gr H4350. So I loaded up the whole range in 0.5gr increments. 41.5gr had no issues. 42 and 42.5 gr I got some pretty good ejector swipe marks, 43 to 44, no more marks, no problems. I never shot the 44.5gr. No signs of primer flattening.

I'm guessing that since H4350 is a slow powder, that the brass was getting shoved back before it could expand tight in the chamber. Any thoughts?
View attachment 19195

 

[sermonator]

Unless your chamber is cut long (which happens), I'm pretty sure that the brass isn't going to move back faster than the cases outward expansion. If that were the case, you'd be seeing some blow-by on the necks of gases coming back along the brass. You're also showing cratered primers. The reality is you may be dealing with the fact that some rifles just don't load up to what the books say. I've got a .257 Imp, that never get's close to what the books list. On the other hand, I had a 7rm, that could load to max and never show signs of pressure. The question is how did your loads shoot? The goal is accuracy, right? Another 30 fps isn't a big deal, is it?

 

[bigedp51]

You do not have swipe marks, swipe marks would happen on a over gassed AR15 when the bolt rotates when there is still pressure in the barrel and force on the bolt face. The marks you are seeing are caused by high pressure and the brass is starting to flow into the ejector. You either have soft cases or your loads are too hot and at approximately 70,000 psi the "normal" pressure that brass begins to flow.

Question, is the rifle a Remington 700?

Case-Head Swipe | Shooting Illustrated

 

[ShtrRdy]

A couple things - Lapua brass in 260 Rem is known for less case capacity. This translates into higher pressure when all else is the same. Also, I'm using about 41 gr of H4350 with a 140 gr bullet in Remington brass. Can you measure the velocity to see where it's running?

 

[Twitch2120]

how do you explain the absence of marks at even higher loadings?

 

[jcampbellsmith]

A couple things - Lapua brass in 260 Rem is known for less case capacity. This translates into higher pressure when all else is the same. Also, I'm using about 41 gr of H4350 with a 140 gr bullet in Remington brass. Can you measure the velocity to see where it's running?

I had success with 142 SMKs, 43.4 gr of H4350, CCI 200 primers and Remington brass (<162gr cases). These Remington cases were specifically selected Remington cases in the 159 gr to 162 gr weight range and had been fired 3 times on my successful test. I didn't use heavier Remington cases for this load. If I was trialing this load again with my Lapua brass I would be starting just below 41 gr and working up. Secondly, I would be using slightly less powder if the brass was new. I typically work up a fire forming load and then rework the load when I'm using my fire formed and full length resized brass.

Regards JCS

 

[BLDTYLRY]

Are you getting heavy bolt lift? What are the the measurements at the neck with a new, loaded, and fired cases? If you can post a photo of the case to include neck, that would be helpful.

I'm running 260Rem Lapua Brass and do not have heavy bolt lift or ejector marks running 140gr A-Max with 45.4gr H4350. My chamber was cut specifically for Lapua brass (.297" necks) by SAC's.

 

[tojan19]

OK, I'll try to hit all the questions.
Yes the rigle is a Rem 700 built by LRI with a Bartlien 5r barrel.

No I didn't chrono, because I left the darn tripod at home. Next time.

I took measurements of my brass. Resized is .294" (using Redding dies with bushings), With a bullet 0.296", fired 0.296-7"



The necks have some soot. The also all seem to have a small nick or dent in the end.

The reamer LRI used for this is 260 REMINGTON TACTICAL MATCH 0.2980 1*30" 0.088 HSS .308W GO (looser neck, throated for heavy stuff in an AI mag).

I never had a hard time opening the bolt and ejecting rounds. A couple of them took a little more effort than normal to close the bolt, I guess that should have told me something, but I was thinking brand new action, and tight neck tolerances.

 

[BoilerUP]

Did you FL size the virgin brass prior to loading it?

I experienced similar issues when I switches from Nosler to Lapua brass in my Criterion 260 and it was a neck tension issue with virgin brass. FL sizing made the problem go away.

 

[6brshooter]

Primers aren't cratered, looks typical rem. Big hole and small firing pin. My tikka sporter 260 was shooting142 smk, nosler brass cci br2, and 44.5 gr of h4350 into bugholes. When i retired the brass with 10 firings on them, some cases were getting donuts, i switched to new lapua. I read about lower case capacity and started at 41.5 gr and same components. Using a chrono i could see that there wasn't much difference between nosler and lapua case capacity. The lapua load that matched velocity,2850, and accuracy,.4s, was 44.1 gr of h4350 . Were u cleaning between each rd OP? Did u dry the chamber after cleaning between rds? If u did no break in then disregard my questions. I forgot a chamber mop once when breaking in a br barrel. Load was a softball load over tge chrony but showed heavy bolt lift and a nasty ejector mark.

 

[Hookman]

TAG - Interested in more info - mine will be built using the same reamer..

 

[tojan19]

The brass was fl resized to mid point on the case gauge.
I clean between did the first five rounds, and after the next five. I did not clean the chamber. The guide I'm using has orings so I don't think the chamber was wet.

 

[6brshooter]

Most bore guides with o rings just keep solvent from getting into the action and bedding. Does ur bore guide go into the nk of the chamber or just seal against the chamber body?

 

[tojan19]

I guess just to the body. It will probably be a few weeks before I can get back to the range I guess I'll just try working up again from a lower charge.

 

[6brshooter]

Err on the safe side, but to me the way the primers aren't even flattened and the fact u were breaking in and not insuring a dry chamber, my bet is on that. This theory would explain why part way through lower charge range, u got ejector marks. When a chamber gets a little solvent in it, it will eventually get dry enough for the brass to grab and not show ejector marks. I had a buddy that after cleaning used clp to protect against rust. Got it doust real good in the chamber. Started getting ejector swipes and heavy bolt lift with factory ammo that was same lot he had been shooting. I figured carbon ring, turned out when he cleaned it he clped the bore/chamber and didn't mop it out. Of course he didn't know a wet chamber would do that but he does now. It took brake cleaner to get all clp residue out and that solcved the ejector marks.