GAP chamber / throat length.

[scout1]

As I posted a month or so ago I received my "modified" Rock from GAP. To say that I'm very happy with it is an understatement. I've been doing my inital load testing at 100 yards and the rifle wants to put the rounds into one ragged hole. I've found this to be the case even if I'm not on top of my game, simply amazing.

Background;
Been shooting for over 40 years and handloading for 35 of those years.

My GAP is chambered for .308 win.

Tools;
Using a Stoney Point overall length gauge and a Sinclair bullet comparator.

Concern:
I've measured my chamber using the above tool and my selected bullet, 175 grain SMK.

My O.A.L. to the lands is 2.785
O.A.L. using the comparator is 3.140

This seems short to me as even factory loads measure in the area of 2.800

All of my handloads have been, from the short side, 2.791 to, on the long side, 2.804. All loads have shot great so far.

My concern and question is, what OAL should I be setting for this chamber/throat length? Seating the bullet at say factory length of 2.800 which puts the bullet well into the lands or seating short of the lands which is well short of even factory length.

This is my first rifle from GAP (won't be my last) and I'm not sure how they cut their chambers.

Also my load so far has been 44.0 grains of Varget with the 175 grain SMK. No overpressure signs at any of the seating depths that I've used.

Any input would help alot.

Thanks, scout1

 

[scout1]

Re: GAP chamber / throat length.

ttt

 

[kombayotch]

Re: GAP chamber / throat length.

Sounds the same as what I got. Load them to 2.775" COAL and drop that charge to 42.5-43 gr. Varget and you will be very happy.

 

[scout1]

Re: GAP chamber / throat length.

kombayotch,
Thank you for the reply. I've also sent an email to GAP but have not heard back from them. You state that it sounds like what you have. Is your rifle also from GAP? Do you know what they recommend? I'm hoping that I receive more feedback on this from this site.

 

[kombayotch]

Re: GAP chamber / throat length.

Yep, also a GAP... they recommend Factory Match loads, just as any and every manufacturer/builder does.

My preferred loads are a 190 SMK seated to that length with either 42.8 gr. Varget or 45.5 gr. RL-17 in Hornady brass or 0.5 gr. less in Lapua brass.

 

[kgreylgrey]

Re: GAP chamber / throat length.

Scout1

Let me stir the pot a little. If you are not seeing any pressure signs and are happy with the speed and accuracy of your load, I'd just shoot it. Suppose, for a minute, that GAP or the Hide recommended a COAL that created pressure signs or dropped your speed/accuracy. Would you switch to that load?

The only negative aspect of jamming a bullet into the lands, as opposed to jumping the bullet, is an increase in peak pressure.

 

[Bronco]

Re: GAP chamber / throat length.

scout, I measured a friends GAP and found the lands at 2.755 with the 175 SMK. He has only shot factory FGMM with no issues. I was concerned but the rifle shoots very well.
Looks to me like you have plenty of reloading experience, work up your loads as usual, if you need to load them a little short so be it. Beats the hell out of having the lands at 2.950.

 

[JRose]

Re: GAP chamber / throat length.

That's wierd. Both of my GAP rifles had a long throat. I would have to seat my bullets out long to get them into the lands. Don't remember the numbers, I have them written down somewhere, but my bullets were .060 from the lands when seated to mag length...

 

[scout1]

Re: GAP chamber / throat length.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LongRanger</div><div class="ubbcode-body">Scout1

Let me stir the pot a little. If you are not seeing any pressure signs and are happy with the speed and accuracy of your load, I'd just shoot it. Suppose, for a minute, that GAP or the Hide recommended a COAL that created pressure signs or dropped your speed/accuracy. Would you switch to that load?

The only negative aspect of jamming a bullet into the lands, as opposed to jumping the bullet, is an increase in peak pressure.

</div></div>
Ken,
Your not stirring the pot at all. However I've been loading long enough to not take random or foolish advice. As for my inquiry I was wondering what is the norm from GAP concerning how their chambers are cut and how others address it. Seating into the lands has been common practice for years so long as pressure signs are OK. I certainly am not saying that I am in favor of it only that it is a practice. As for the rifle, the damn thing just shoots. By far the most forgiving rifle that I have ever shot reguardless of load.

 

[armada]

Re: GAP chamber / throat length.

I think it depends on what you tell GAP when you ordered the rifle. I remember all the rifles I had them build, George asked me what it was going to be used for and if I had a bullet preference. Then he proceeded to ask me even more questions on use and so on. I'm sure he would cut the throat based on the information he/they were given. Just my .02.

 

[knockemdown]

Re: GAP chamber / throat length.

In my love letter to GAP for my .243 build, I specified my bullet preference (115DTACs) and mag system (Seekins DMS)...

My rifle came back to me throated accordingly. A 115DTAC hits the lands at 2.780 c.o.a.l. Plenty enough room for 4350 inside and plenty of elbow room in the magazine to boot...

 

[HotIce]

Re: GAP chamber / throat length.

In my GAP 308, using a Stoney Point and Scenar 167gr, I get 2.787" OAL when touching the lands.
Rifle is accurate when loaded with 167gr Scenar at that OAL, so I've no complains.
I take the measure every 100-150 rounds to adapt accordingly. When new, OAL with 167gr was 2.782".
Next time I'll ask a longer throat though.

 

[calbearz]

Re: GAP chamber / throat length.

Hi Scout1

I have a GAP in .260 Rem. I have found that GAP seems to cut their chambers for VLD type bullets. I started out with 120 gr speer soft points (not VLD) and I seated to 2.800, turned my gun into a $3500 bullet puller because closing the bolt jammed the bullet into the lands so hard it would pull the bullet if you opened the bolt. By contrast when using VLD bullets seated to 2.800 are just kissing the lands, and shooting 0.25 inch groups at 100 yards. I guess its just a compromise but it does allow you to use VLD seated to magazine length and have them close to the lands. Hope this helps.

 

[Rothbard73]

Re: GAP chamber / throat length.

Assuming that your GAP and the Crusader have the same chamber, you could call or email Pacific for a copy of the schematic (541)826-5808

My Crusader's chamber was done with the Pacific Tool "308 Palma Match" reamer. I emailed them and they sent me the schematic. Just ask them for a copy of the GA precision/308 Palma Match print. It will have all of the info you need. My Crusader loves the 175 SMK's. With the 175's, using the Hornady lock-n-load and their caliper attachment to measure the distance to the lands I get a Max length to the lands of 2.81" w/175 smk, and a Max OAL of 2.866. My pet load has been the following:

175 SMK, seated 0.020" off the lands(2.260" w/ Hornady gauge) Lapua brass
44.6 gn Varget
Fed 210m
2650 fps

 

[jeffbird]

Re: GAP chamber / throat length.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Nietzsche73</div><div class="ubbcode-body">
175 SMK, seated 0.020" off the lands(2.260" w/ Hornady gauge) Lapua brass
44.6 gn Varget
Fed 205m
2650 fps </div></div>

Nietzche,
Just double checking, buti is F205 i.e. small rifle primer correct info, or was that a typo? Doesn't a 308 case need a 210 - a large rifle primer, or the 215M, the large rifle magnum primer to fit in the case?

 

[tgm1175]

Re: GAP chamber / throat length.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jeffbird</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Nietzsche73</div><div class="ubbcode-body">
175 SMK, seated 0.020" off the lands(2.260" w/ Hornady gauge) Lapua brass
44.6 gn Varget
Fed 205m
2650 fps </div></div>

Nietzche,
Just double checking, buti is F205 i.e. small rifle primer correct info, or was that a typo? Doesn't a 308 case need a 210 - a large rifle primer, or the 215M, the large rifle magnum primer to fit in the case? </div></div>

Yes, a 308 uses large rifle primers.

 

[Rothbard73]

Re: GAP chamber / throat length.

Yes, its a typo! I should've wrote 210m.

 

[SuperXJeff]

Re: GAP chamber / throat length.

Your rifle is cutting bullet holes. You are done. Let them jump or jam them? I let them jump just because they usually feed easier. If jamming them produces no feeding issues then jam them. I shoot Remington 700's often with sloppy chambers on the very long side of SAMMI specs. Still with my factory chamber and shells loaded to book overall length since there is no way on earth I could reach the lands the gun shoots 1/4 to 1/2 MOA.

I think it all depends on the gun. There are no hard and fast rules on length except that each gun is it's own little mystery. I have one .300 barrel that was cut with a new match grade reamer that we also reamed a section of barrel so we know exactly what the chamber measures. Th gun shoots best 5 thousandths off the lands. You just never know... Like Longranger said, Into the lands you may have a little higher pressure so all things being equal I would go with the length that should produces the lowest pressure. Good luck Jeff

Be happy your gun shoots in one hole. Jeff