260 Remington: How limited will I be by mag legth?

[nuclear_shooter]

Thinking of building my AR-10 in 260 rem (as I've posted about before). Before ordering a barrel, I want to know how limited I will be by loading to magazine length. I realize that I can top feed an AR style rifle, but if I wanted to do that I'd just grab a bolt gun. Specifically wondering if anybody has had good success loading 140 gr hybrids or amaxs in a pmag?

I realize this question is born out of totally ignorance, but I haven't found much info online. I just want to go into this with a good idea of what bullet(s) I will want to shoot. This also may be better suited for the reloading forum... Thanks!

 

[LRRPF52]

I've been trying to dispel the perception about there being limitations with the .260 Rem in the AR-10, and I've owned 2 of them, with my current one being a Bartlein-piped custom rifle from GA Precision before the GAP-10 was available.

140gr A-MAX's are no problem.
142gr SMK's
139gr Scenars
130gr VLD's
130gr Norma Golden Target
123gr Scenars
140gr Match Burners



They all work fine. I like the 130gr VLD and Norma's for the speed and great BC so far. I push them over 2800fps from a 22" barrel.

The real limiting factor is the firing pin hole size, and I wish I had my old Armalite to work with in this regard, or Armalite BCG's. The DPMS guns have a larger hole that will experience cratering earlier than the Armalite, being that the .260 Rem is a 60,000 psi SAAMI case.

If you are looking for good semi-auto long-range performance out past 1000yds, I think the AR10 is better served with .260 Rem than most other chamberings, and is an easy build or conversion requiring only a barrel swap.

 

[nuclear_shooter]

I've been trying to dispel the perception about there being limitations with the .260 Rem in the AR-10, and I've owned 2 of them, with my current one being a Bartlein-piped custom rifle from GA Precision before the GAP-10 was available.

140gr A-MAX's are no problem.
142gr SMK's
139gr Scenars
130gr VLD's
130gr Norma Golden Target
123gr Scenars
140gr Match Burners



They all work fine. I like the 130gr VLD and Norma's for the speed and great BC so far. I push them over 2800fps from a 22" barrel.

The real limiting factor is the firing pin hole size, and I wish I had my old Armalite to work with in this regard, or Armalite BCG's. The DPMS guns have a larger hole that will experience cratering earlier than the Armalite, being that the .260 Rem is a 60,000 psi SAAMI case.

If you are looking for good semi-auto long-range performance out past 1000yds, I think the AR10 is better served with .260 Rem than most other chamberings, and is an easy build or conversion requiring only a barrel swap.

Great info. Out of curiosity, did you use a special reamer to cut the lands a little bit closer?

As for the BCG, I hadn't really decided, but I looked at the 7.62 Industries offering. Heard some negatives about it, but a friend has one and it seems to run just fine. Could you get the hole bushed?

 

[LRRPF52]

I did ask Jeff at GA Precision to cut the chamber for the 139gr Scenar, but it also shoots the VLD's so well, that all the advice I was given about VLD's not shooting in a gas gun flew out the window.

A lot of my starting loads I test at 500yds-no reason to screw around at 100 now that I know what the gun will do. I'll guestimate my drop, knowing that I'll be on paper at least, and several times have center-punched, and I mean dead-center punched plates and paper with it at 500yds. 500yds is a waste of .260 Rem capabilities, unless in competition, and even 700yds is boring. You have to find really small targets to make it challenging at distance.

Here's my recent work with 130gr Norma GT:

130gr Norma GT & IMR4831
Winchester Large Rifle (not sure why I used this one, as I normally use Rem 9 1/2)
IMR4831
Lapua .260 Rem brass 1 x fired
42.5gr 2770
43.0gr 2824
43.5gr 2833
2.810" COL

130gr Norma GT + H4350
WLR primer
Lapua 1 x fired
2.810" COL
42.0gr was too hot cratered primers, ejector extrusion, debris embedded in the primer

2855
2824
2879
2851

54.43 ES
19.51 SD

 

[bullseye13]

I had a DPMS LR260 when they first came out, and I was very unhappy with the chamber in that gun. I used it for hunting, and with a 130gr Swift scirocco's loaded at mag length, I was still .120 of the lands. It shot those terrible. 100gr, and 120gr ballistic tips shot fine. Ended up selling it. I wouldn't do it again without having the chamber cut for my needs.

 

[LRRPF52]

I started with the DPMS LR-260 as well. I think they used a chamber meant for tangent ogive 120gr, loaded out, so there is a lot of jump using more secant ogive pills.

.260 Rem should have a VLD chamber, even for hunting guns, since so many of the better hunting pills have more modern ogives, especially the 129gr Hornady SST and IB's, Swift Scirocco's, the new 129gr Nosler Accubond LR, the 140gr SST, etc.

 

[nuclear_shooter]

I started with the DPMS LR-260 as well. I think they used a chamber meant for tangent ogive 120gr, loaded out, so there is a lot of jump using more secant ogive pills.

.260 Rem should have a VLD chamber, even for hunting guns, since so many of the better hunting pills have more modern ogives, especially the 129gr Hornady SST and IB's, Swift Scirocco's, the new 129gr Nosler Accubond LR, the 140gr SST, etc.

I definitely think it comes down to getting the right chamber cut. Generally they're cut long to accommodate a wide range of bullets. I just wanted to make sure it was possible to load em a bit further back to fit in the mag without making something go boom.

I will need to do a bit of research on what reamer to use for the barrel. I know if you send PTG a dummy round or two they'll make you a reamer for it, but I dunno about any of the other dimentions, esp for a gas gun. I don't suppose you want the neck to be real tight to allow good feeding.

I'm also considering going with a JP barrel, if anybody has any experience with the heavier bullets in this barrel, I'd appreciate input.

 

[LRRPF52]

I started using necked 7mm-08 brass, which I really like. When I switched to Lapua, I learned the hard way that I needed to size all my cases before firing, as my neck is pretty tight in my chamber.

.260 Rem SAAMI is .297" for the neck. Fired cases measure .295" - .293" from my gun.

No worries about making anything boom, unless you use pistol powder. JP .260's have a great reputation.

 

[nuclear_shooter]

Good stuff. How reliable is your gun?

 

[LRRPF52]

The only malfs I have had were with the ejection port door closed for the first round fired, and the new Lapua brass that wasn't sized, right in the middle of a match.

Makes me wonder if the ejection port spring isn't strong enough. Chris Kyle said something similar about the Mk.11's he was using with the ejection port door closed malf.

I noticed that HK used a plastic port door on the 417. Maybe this has something to do with that.

 

[Newtrick]

I'm loading 140 gr Amax's at 2.826 OAL. Just fits. In the mag, and in about .6 of an inch.

 

[elfster1234]

im just wondering, how much of a jump are we talking about on average? ballpark.

I've been trying to dispel the perception about there being limitations with the .260 Rem in the AR-10, and I've owned 2 of them, with my current one being a Bartlein-piped custom rifle from GA Precision before the GAP-10 was available.

140gr A-MAX's are no problem.
142gr SMK's
139gr Scenars
130gr VLD's
130gr Norma Golden Target
123gr Scenars
140gr Match Burners



They all work fine. I like the 130gr VLD and Norma's for the speed and great BC so far. I push them over 2800fps from a 22" barrel.

The real limiting factor is the firing pin hole size, and I wish I had my old Armalite to work with in this regard, or Armalite BCG's. The DPMS guns have a larger hole that will experience cratering earlier than the Armalite, being that the .260 Rem is a 60,000 psi SAAMI case.

If you are looking for good semi-auto long-range performance out past 1000yds, I think the AR10 is better served with .260 Rem than most other chamberings, and is an easy build or conversion requiring only a barrel swap.

 

[nuclear_shooter]

im just wondering, how much of a jump are we talking about on average? ballpark.

I would guess that would depend on how the chamber was cut. I may email JP and ask them how their chambers are cut. Maybe they take requests?