I've been working on a fun project lately!
6.5 LRM
Guys have been having great fun with 6.5SAUM, but those tend to not feed very well out of unmodified Desert Tech magazines. So in response, I wanted to find a good candidate in the 6.5 magnum variety for DT users. We've chambered a few in 26 Nosler, and they've been absolute hammers. I think if someone wanted a turn-key hardcore 6.5, the 26 nosler is probably the go-to in a SRS or Covert. However, all that speed comes at a price. There is no denying that the 26 nosler is a barrel burner.
I'm running a 30" 8 twist TS Customs barrel with heavy contour. I have this same configuration in a 7LRM barrel.
I start out with factory Gunwerks (hornady) 7LRM headstamp brass. Upon close inspection, the neck has about .0015 to .002" of brass thickness taper from the neck/shoulder junction to the top of the case mouth. That's quite a lot of thickness variation that I didn't care for, so I got a batch of brass turned to .0145"-.0150" uniform thickness. That gave me a barely measurable uniformity variance from shoulder to mouth of about half a thousandth with the necks around 80%+ cleaned up. Some cases were absolutely horrible... but given the very proprietary nature of this cartridge, I can forgive that. Runout on the case mouth ran from .0015 to as much as .005" with most of the cases being in the .002-.003 range.
Sadly I don't yet have a FL die for the 6.5LRM, so I used a 7LRM bushing die to size the necks. This unfortunately left the case largely unsupported, which induced as much as .008" of runout with an average of about 5 thousandths. After scavenging a 6.5mm expander I was able to get that down to about .003 which isn't the end of the world. On the turned brass, a .291 bushing turns out to be the right stuff. I stepped it down in two op's, with the first pass at .305 and the second pass with the .291\. I think 3 passes with smaller steps in diameter would have helped with the runout issue. The 7LRM brass starts off at about .315 to start with... so going to .291 is a 24 thousandths squeeze and I usually don't like to take bigger than about .008" steps when sizing down without a custom FL die. In any event, I cruised through that discovery process and got a sizing method down that was acceptable.
First I went to work with 140gr Berger VLD's. I was met with dismal results. I threw everything but the kitchen sink at it. Over a hundred twenty thousandths + of seating depth, 4 different powders, neck tension... on and on. Nothing would get those picky VLD's to behave. Then I grabbed some Berger 140 Hybrids... and boy oh boy did it come alive. Quarter MOA groups and better, and it really didn't much matter where they were seated or what charge weight of whatever powder I tried. I settled on a BTO of 1.720", putting me about .010" off the lands. H1000 seems to be a winner.
Here are some velocities at varying charge weights:
H1000 velocity
62gr - 2895
64gr - 3040
66gr - 3108
68gr - 3190 - pressure just starting
It isn't as if this cartridge will be creating a revolution like the 7LRM has done, although it is certainly a neat option for folks looking for something a little different than the available offerings. So far I seem to be settled in right around the 66gr mark, but there's more work to be done. I've got just over 135rnds down this barrel, so it will be interesting to see what goes on with velocity as things settle in. Feeds like a dream in my DT SRS-A1 and gives me some solid performance with the expectation of reasonable barrel life.
6.5 LRM
Guys have been having great fun with 6.5SAUM, but those tend to not feed very well out of unmodified Desert Tech magazines. So in response, I wanted to find a good candidate in the 6.5 magnum variety for DT users. We've chambered a few in 26 Nosler, and they've been absolute hammers. I think if someone wanted a turn-key hardcore 6.5, the 26 nosler is probably the go-to in a SRS or Covert. However, all that speed comes at a price. There is no denying that the 26 nosler is a barrel burner.
I'm running a 30" 8 twist TS Customs barrel with heavy contour. I have this same configuration in a 7LRM barrel.
I start out with factory Gunwerks (hornady) 7LRM headstamp brass. Upon close inspection, the neck has about .0015 to .002" of brass thickness taper from the neck/shoulder junction to the top of the case mouth. That's quite a lot of thickness variation that I didn't care for, so I got a batch of brass turned to .0145"-.0150" uniform thickness. That gave me a barely measurable uniformity variance from shoulder to mouth of about half a thousandth with the necks around 80%+ cleaned up. Some cases were absolutely horrible... but given the very proprietary nature of this cartridge, I can forgive that. Runout on the case mouth ran from .0015 to as much as .005" with most of the cases being in the .002-.003 range.
Sadly I don't yet have a FL die for the 6.5LRM, so I used a 7LRM bushing die to size the necks. This unfortunately left the case largely unsupported, which induced as much as .008" of runout with an average of about 5 thousandths. After scavenging a 6.5mm expander I was able to get that down to about .003 which isn't the end of the world. On the turned brass, a .291 bushing turns out to be the right stuff. I stepped it down in two op's, with the first pass at .305 and the second pass with the .291\. I think 3 passes with smaller steps in diameter would have helped with the runout issue. The 7LRM brass starts off at about .315 to start with... so going to .291 is a 24 thousandths squeeze and I usually don't like to take bigger than about .008" steps when sizing down without a custom FL die. In any event, I cruised through that discovery process and got a sizing method down that was acceptable.
First I went to work with 140gr Berger VLD's. I was met with dismal results. I threw everything but the kitchen sink at it. Over a hundred twenty thousandths + of seating depth, 4 different powders, neck tension... on and on. Nothing would get those picky VLD's to behave. Then I grabbed some Berger 140 Hybrids... and boy oh boy did it come alive. Quarter MOA groups and better, and it really didn't much matter where they were seated or what charge weight of whatever powder I tried. I settled on a BTO of 1.720", putting me about .010" off the lands. H1000 seems to be a winner.
Here are some velocities at varying charge weights:
H1000 velocity
62gr - 2895
64gr - 3040
66gr - 3108
68gr - 3190 - pressure just starting
It isn't as if this cartridge will be creating a revolution like the 7LRM has done, although it is certainly a neat option for folks looking for something a little different than the available offerings. So far I seem to be settled in right around the 66gr mark, but there's more work to be done. I've got just over 135rnds down this barrel, so it will be interesting to see what goes on with velocity as things settle in. Feeds like a dream in my DT SRS-A1 and gives me some solid performance with the expectation of reasonable barrel life.
