260 cycling issue

[HotRod308]

I have a friends DPMS 260 Rem hunter rifle that is not working right. 20 inch barrel and rifle length gas system. With a 120g bullet and 42.5 g of H4350 the bolt cycles and locks back just fine. With 44.5g H4350 and the 120g bullet it will cycle back far enough to pick up a round but not lock back.

I'm thinking the higher charge of powder has increased velocity to the point that the bullet is gone before the received a full charge of gas pressure to cycle the bolt. With the slower bullet it has not left the barrel allowing the gas system to work correctly.

 

Is my line of thinking off or not? Drill the gas port a little larger or put in a softer spring? 

[unforgiven]

Maybe a heavier buffer to increase reciprocating action....just a thought.

[shepp]

Drill out the gas port would be my last resort I think. I'm sure some one like SS or 98 will come drop some knowledge 

[98Z5V]

11 hours ago, HotRod308 said:

I have a friends DPMS 260 Rem hunter rifle that is not working right. 20 inch barrel and rifle length gas system. With a 120g bullet and 42.5 g of H4350 the bolt cycles and locks back just fine. With 44.5g H4350 and the 120g bullet it will cycle back far enough to pick up a round but not lock back.

I'm thinking the higher charge of powder has increased velocity to the point that the bullet is gone before the received a full charge of gas pressure to cycle the bolt. With the slower bullet it has not left the barrel allowing the gas system to work correctly.

I think you're on to something there.  Same bullet (120, lighter charge by two full grains will lock it back. In theory, with a charge two full grains higher, you should be producing quite a bit more power, speed, and gas pressure. The rifle should cycle even harder, have more felt recoil, and lock-back on last round should be easy like that.

But, it's not.  Because that extra two full grains of pressure isn't getting there, through a small gas port that won't allow it. Instead, the bullet is gone from the barrel, and pressures drop. 

Pull the gas block and measure that gas port.  I don't know schit about .260 Rem gas port sizes, but I'm curious to see what it is anyway.

[HotRod308]

Yes, I found that I have aprox a .069 gas port. I compared it to a 6mm wildcat barrel takeoff that I have and that gas port was aprox .079 in dia. The port was also 2 inches further down from a standard rifle length port location as the barrel was 26 inches long.

Planning on drilling the hole bigger to .077 as it is the next size drill bit that I have.

Any thoughts? I have an adj gas block in case it cycles to hard.

[HotRod308]

Yes, I found that I have aprox a .069 gas port. I compared it to a 6mm wildcat barrel takeoff that I have and that gas port was aprox .079 in dia. The port was also 2 inches further down from a standard rifle length port location as the barrel was 26 inches long.

Planning on drilling the hole bigger to .077 as it is the next size drill bit that I have.

Any thoughts? I have an adj gas block in case it cycles to hard.

[HotRod308]

I wonder if other cycling problems people have with short 18 - 20 inch barrels have the same problem when shooting lighter weight bullets? Bullets leaving the barrel before the action has a chance to operate before the bullet has left the barrel.

In one post the factory rep/tech told the owner to shoot 168g bullets or bigger to have the rifle to cycle.

Just a thought.

[washguy]

Yep,you are on the right track.....drill it out        Wash

[survivalshop]

  To me, the 2 extra grains of the same powder , with the same Bullet , same Barrel ,would produce a much higher barrel pressure & would cycle the action with much more force with the higher gas signature . Saying that , it is possible that the larger charge of Powder in the case , could actually lower chamber & barrel pressure ( before the Gas Port )  , because more powder is burnt ( or unburnt ) farther down the barrel . Different cartridge case volumes & Bullet diameter's can produce some odd characteristics . 

  I would try different power (s ) , magnum Primer maybe , if possible , I know nothing of this Caliber , so I have no experience with Powder choices . 

 Is the recoil more stout with the ammo & its extra Powder charge  ? 

 Making the Port larger would be last thing I would do , because you can't go back , not that the end result wouldn't need it done .

[washguy]

Check out the blueprints on this ...port is .093                    Wash

 

Lilja Precision Rifle Barrels

 

http:/criflebarrels.com/wp-content/uploads/ar1024_w_ext_mod.pdf

 

... A Krieger 6.5 Creedmoor has a .086" port, RLGS and .936" journal. Bartlein uses .086" for 6.5 CM and .260 Rem as well.

 

drill it

 

Edited October 10, 2016 by washguy

[ARTrooper]

man if Krieger and bartlein use .086", that's like the word of God right there when it comes to barrels. :P

[HotRod308]

excellent info, .096 port. Will post after I shot it on Sat

[ARTrooper]

don't drill it to big right away, better to work your way up. remember, you can always drill more, but you can't undrill.

[ARTrooper]

hoping you saying ".096" was a typo and you meant .086. lol.

[DNP]

6 minutes ago, ARTrooper said:

hoping you saying ".096" was a typo and you meant .086. lol.

Go big or go home, right?  Could always throw one of those fancy adjustable blocks on if it was too much.  Don't forget Wash's favorite tip about putting a wood dowel down the pipe for a little protection. 

[ARTrooper]

well if it is good enough for krieger and bartlein, it would be good enough for me since they make some of the best barrels in the world that many professionals use. if it still needs drilling after that, he can always go up to the .093 of lilja barrels.

you probably know better, I just like to play it safe.

let's see what wash says. lol.

[washguy]

Yeppers..wooden dowel  like DNP sez in the barrel...better to spit wood than metal on the otherside....start small..go bigger.if need be.

always use numbered drill bits  
                       #46 is.0810                #45 is .0820     #44 is.0860  #43 is .0890    #42 is .0935  #41 is.0960   #40is.0980

 

found another tid bit      

Re: .260 Gas Port Dimensions

.081 port for .260, 20" Barrel, std rifle length gas tube.

saw where the Tubbs spring does good in a .260.....thats my go to spring for anything    my crystal ballz sees a Tubbs spring and adjustable gas block in your future         Wash

Edited October 11, 2016 by washguy

[DNP]

I don't know crap...just what I read on the internet sometimes. And the Internet is always right! I'd go with wash...he's been right a few times before. 

[jtallen83]

Double check your bit sizes. The set I bought had numbers that didn't match what the chart said they should be, I ended up going by the measurements my caliper told me instead of the chart.

[ARTrooper]

oh man, never thought about that jtallen. good thing you realized that. now I am gonna be paranoid about my tools. lol.

54 minutes ago, washguy said:

start small..go bigger.if need be.

yup, kinda the same thought as measure twice, cut once. better to take a little longer and get it right than take to much off.

[washguy]

57 minutes ago, ARTrooper said:

oh man, never thought about that jtallen. good thing you realized that. now I am gonna be paranoid about my tools. lol.

yup, kinda the same thought as measure twice, cut once. better to take a little longer and get it right than take to much off.

Yep and just leave the rail off the barrel while tuning in if you can,so you dont have to keep reassembling the rifle   always always it must lock back on single round, and feed another of course       Wash

[beantown]

3 hours ago, ARTrooper said:

hoping you saying ".096" was a typo and you meant .086. lol.

You beat me to it.

[ARTrooper]

when I saw it, I figured someone better jump at it quickly so no errors bigger than a typo was made. haha.

[survivalshop]

    Has there been any factory ammo shot through this rifle & if there was , how did it work ? 

[HotRod308]

Been busy these past day or so, had to testify in court against a drunk driver yesterday.

Anyway, thank you all for the help and info and all the tips. I due have a wooden dowel in place and still need to check a few stores on drill bit options. I have a 5/64 and I believe a 3/32  drill bit. The 3/32 is a .093 drill bit and a 5/64 is .078 .  Going to look for a drill bit in between and stay with drill small and work my way up.

I never tried any factory ammo in the rifle. But the loads that did lock the bolt back at the very low end of starting charge for H4350 and the bullet weights that fired through it. Based what I read and shooting the rifle its not getting enough gas fast enough before the bullet leaves the barrel. 

Hopefully I will have this done and try it at the range soon this weekend.

 

Thanks again