Seat Depth for .308 Win

[l115a3]

Hi,


Which seat depth will create higher pressurse & bullet speed?

.020 Jump (COAL = 2.840")
.060 Jump (COAL = 2.800")


Remington 700 XCR Compact Tactical .308 win
1:12tw 20" Factory Barrel
Lapua Brass
Federal GM210M Primer
43.0 Grains of Varget
.30 Sierra 168 Gr. SMK

 

[boltgunluvr]

Re: Seat Depth for .308 Win

Tricky question!!!!

 

[MitchK]

Re: Seat Depth for .308 Win

I would say the shorter coal would give you higher pressure, unless your longer load is jammed in the lands.

 

[l115a3]

Re: Seat Depth for .308 Win

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchK</div><div class="ubbcode-body">I would say the shorter coal would give you higher pressure, unless your longer load is jammed in the lands. </div></div>


Hope my friend take my CEDM2 to the range today for test.

 

[Jim Buck]

Re: Seat Depth for .308 Win

Depends on if it's jammed, if so the 2.84.

 

[Temp9]

Re: Seat Depth for .308 Win

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchK</div><div class="ubbcode-body">I would say the shorter coal would give you higher pressure, unless your longer load is jammed in the lands.</div></div>

Agreed. Shorter COAL will lower the initial expansion volume, so should slightly increase the initial pressures.

 

[thefitter]

Re: Seat Depth for .308 Win

I doubt that 2.84 would be jammed on a factory chambered barrel.

 

[jwp6114]

Re: Seat Depth for .308 Win

take note...

less jump = higher inital pressure. Higher initial pressure = cases ware out faster. I prefer to to build my velocity in the barrell, more jump with a slower burning powder in longer barrels, so their are several factors that contribute to velocity.

I use .008 jump in my gun, with stronger brass like norma or Lapua brass life is higher.

 

[Fuzzball]

Re: Seat Depth for .308 Win

<span style="font-style: italic">"Which seat depth will create higher pressurse & bullet speed?"</span>

It's not that easy. Rifles don't follow the same seating rules for small, high pressure handgun loads. Seating deeper in rifles allows for easy bullet start and a lot of bullet speed/inertia to help it engrave the rifling; that reduces the peak pressure, sometimes quite a bit. But, that's as far as a generalization can take you. Seating at or into the lands impedes initial bullet movement and that makes the ignition part of the pressure:time curve change - a lot.

Longer OAL will increase peak pressure but the effect on velocity is much more complex and can't possibly be answered with a simple 'this or that' statement. Other than a simple peak pressure change, a few of the more easily seen variables include case capacity, quanity and burn rate of the powder, barrel length, bore diameter, bullet weight. And, perhaps, which way the ducks are flying. Meaning, if you really want to know the answer to your question you're gonna have to test it for yourself.

 

[Highflyer]

Re: Seat Depth for .308 Win

Les Baer recommends .035 jump. OAL 2.800 or slightly under. The same as factory match.

 

[l115a3]

Re: Seat Depth for .308 Win

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: thefitter</div><div class="ubbcode-body">I doubt that 2.84 would be jammed on a factory chambered barrel. </div></div>

Not jam with Remington 700 XCR factory chamber sir.

I think they do not use a tight chamber as match chamber and it was a mass production. Some guys found COAL to touch the land over 2.9"

As I tried with RCBS MIC, my XCR COAL for just touch the land was 2.860" with 175 SMK.

 

[l115a3]

Re: Seat Depth for .308 Win

Hi,


I just got the chamber detail form Dave Kiff.

LB Tactical Recon Bolt Rifle was using PTG reamer with .088 FB due to they required for feeding from magazine.


They were take their bolt rifle out of production due to lack of time.


Regards,
Golf

 

[Deadshot2]

Re: Seat Depth for .308 Win

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Golfy Sniper</div><div class="ubbcode-body">

LB Tactical Recon Bolt Rifle was using PTG reamer with .088 FB due to they required for feeding from magazine.


They were take their bolt rifle out of production due to lack of time.


Regards,
Golf </div></div>

More likely they returned to their core competency, pistols. For the price they wanted for what didn't shoot better than a 5R Milspec in the same B&C A-5 stock, sales were probably no where what they expected.

As for which COAL to use I've found that my rifles respond far better to first finding a load that is as accurate as can be with a 2.820"COAL to start. Once I find that load, I then play with the OAL in .005" increments until I have optimized the basic load. If I vary from that process I usually end up chasing my tail until I risk disappearing up my a** h****. Fine tuning requires single changes only.

 

[YAOG]

Re: Seat Depth for .308 Win


Golf,

Did you get to chrono that 168SMK load? Seems like it would be pretty slow given the components listed and the low powder charge. Do you know how many grains of H2O your cases hold?

 

[DanSavage]

Re: Seat Depth for .308 Win

2.800 would give slightly more pressure.

 

[infinitegunner]

Re: Seat Depth for .308 Win

I'm running 2.84 in my FN SPR with excellent results 43.7 gr. Varget.