Well below OAL but still hitting Lands

[timbrline]

Working up a load for Sierra 180 TGK’s in .308.

Using 4064, typical stuff I’ll spare you all the details.

I started with full length sized cases trimmed to spec. Nothing fancy.

Seated bullets to 2.800” OAL...

Barrel is JP supermatch with lmos bolt/group.

Bullets jam into lands when chambered.

Seated all the way down to 2.75”.. bullets jam into lands... hard enough not only are they marked they actually get stuck in the chamber.

Now... m118lr’s shoot great... and I never even thought to look until this happened, however, I cycled a few through and they have mild scoring marks from lands as well.

This a defunct chamber?? JP didn’t reply to a request for info from them. Just looking for thoughts.

I thought finally maybe it was just cut for a light round... cycled a couple 165 BTSP federal through.. light marks on the bullets from the lands....

What gives fellas? Ideas?

 

[seanh]

I'm guessing either your measurements are off or simply different bullet shape gets the actual bullet touching the lands sooner.

Get a bullet comparator to see the difference between the two cartridges

 

[Jordanwickham]

My factory 6.5 CM had a 60k jam with 140 SMKs loaded to 2.800" I had to load them at 2.720" to have a 10 k jump. I don't know about that chambering I'm guessing that is a high performance chambering? It may be more of a secant / hybrid chambering rather than a tangent. Have you tried a secant or hybrid bullet?

 

[isofahunter]

Measure to Ogive not OAL. Measure Ogive of the M118LR and make you load match that measurment and it should work. Similar experience with TMK when I used them.

 

[clcustom1911]

Each bullet type will contact the lands at a different length because the ogive shape is different. A sleek, ling nose 175 matchking's bearing surface and ogive length are different that a more short-nosed 180 game king. You need to adjust your OAL for you optimal jump for each bullet you use.

For instance, if you want the 180 to jump the same 0.020" as the 175, you may need to seat the 180 at 2.72 because it is a different shape than the matchking.

Does that make sense?

Edit to add...

Each bullet that I use for all my rifle cartridges have a different OAL based on where the ogive/bearing surface junction touch the lands. For example, for my Tikka T3x Tac A1, my 130g Berger is as 2.78" or so, and my 142 MatchKing's are at 2.80, my 147 ELDm is at 2.86 all because they are different shaped bullets.

There's an article in the sticky section here that describes it perfectly:

Hand Loading for Long Range 3: finding start OAL

Chapter 3: "Where’s my rilflings and where should I put them?" So having prepped and primed our brass & sorted our bullets into identical lots now we need to know at what overall length we need to seat the bullet into the case. How do we figure that out? Well there are a few ways to establish a...

www.snipershide.com

 

[timbrline]

I should have prefaced this a bit more. I get the OAL concept. With a TGK the profile is supposedly similar to the SMK, just with a tip. I started the work up with an empty, seating it deeper to the right jump. But, when I’m jamming a 180g bullet in a .308 down to 2.72” OAL... and it’s still engaging hard enough on chambering it’s getting stuck... I got a little concerned. Sierra has not posted load data for the 180 TGK... in contacting them, their tech said they were just using data for the 180 HPBT Match with equal results....

I just don’t see data on any match profile round in .308 that’s getting down to the 2.7 OAL.... when do pressures start getting sketchy. Running 4064 at 40.6g-41g test loads... that 180 is compressing that charge that deep.

So... crap... lot going on with thing. JP says they do not use a tight reamer at all, even on supermatch barrels as it just isn’t conducive good function, which we know.

I’ll keep playing with it. Reduce the charge a little and seat deeper ... see what MV and Pressure I get.

I’d really like to get these 180’s running... I don’t know why... maybe a new bullet is a challenge and just pissed me off! Haaaa.....

 

[clcustom1911]

Do you feel/hear crunching as you're pressing the bullet in the casing?

What brass are you using?

 

[Jordanwickham]

I should have prefaced this a bit more. I get the OAL concept. With a TGK the profile is supposedly similar to the SMK, just with a tip. I started the work up with an empty, seating it deeper to the right jump. But, when I’m jamming a 180g bullet in a .308 down to 2.72” OAL... and it’s still engaging hard enough on chambering it’s getting stuck... I got a little concerned. Sierra has not posted load data for the 180 TGK... in contacting them, their tech said they were just using data for the 180 HPBT Match with equal results....

I just don’t see data on any match profile round in .308 that’s getting down to the 2.7 OAL.... when do pressures start getting sketchy. Running 4064 at 40.6g-41g test loads... that 180 is compressing that charge that deep.

So... crap... lot going on with thing. JP says they do not use a tight reamer at all, even on supermatch barrels as it just isn’t conducive good function, which we know.

I’ll keep playing with it. Reduce the charge a little and seat deeper ... see what MV and Pressure I get.

I’d really like to get these 180’s running... I don’t know why... maybe a new bullet is a challenge and just pissed me off! Haaaa.....

I'd definitely suggest not running a .4 grain test string. How much compression are you getting? Bad enough that you are getting inconsistent seating depth? How much of the bearing surface is in the neck?.

 

[MakeSawdust]

I personally think something is going on with the chamber that is funky. It could be caused by any number of things. The internal dimensions of the blank could be slightly wierd, the chamber could be crooked, or any number of things. I have had "same blank, same reamer" barrels where the seating depth was pretty different to touch the lands. These were all with mass chambered Criterion savage prefits on bolt guns. My wife also has a 6 Dasher barrel where there are partial lands extending all the way back to the cartridge neck. I went through things with the gunsmith and we were both scratching our heads. The reamer was a .150" freebore and we were comparing lengths on other barrels in his shop over the phone that had been cut with the same reamer. I gave up and loaded the bullets touching. The gun hammers, so I never pushed the issue. Once I bought a borescope I could see what the deal was.

If you can get it to shoot I wouldn't worry. If it causes issues, I would look with a borescope and see if anything about the chamber looks goofy.