Semi-Auto reloading ( .308 )

[Egonzalez3]

I am very new to reloading, and find very little to nothing on semi-auto reloading. Manuals are created for bolt action, and SAMMI C.O.A.L (2.80) is smaller than what I measured to the lands on my HK MR762 - currently @ 2.941. Using Lapua palma / 168 Sierra TMK / CCI BR4 primers.

First time loader

 

[2aBaC̶a̶]

Imho, its the 98% same as loading bolt gun. Saami and reloading book spec is a good start. Typically bump the shoulder on fired cases a little more than bolt guns. Bullet length can depend on what fits in a mag and what will feed reliably. It's more about finding what your gun likes.

 

[918v]

Load them to mag length.

With regard to shoulder length, don’t bump more than for a bolt gun. First find zero clearance length, then load a dummy round, and let the bolt feed it into the chamber from the magazine. Then measure the shoulder length again. Your rifle might be bumping the shoulder during chambering.

I recently tested my AR10 and it is bumping the shoulder .004” from the mag and .007” if I just drop one in the chamber and let the bolt fly.

As a result of that test I now bump the shoulders .002” just like for my bolt gun.

 

[2aBaC̶a̶]

Load them to mag length.

With regard to shoulder length, don’t bump more than for a bolt gun. First find zero clearance length, then load a dummy round, and let the bolt feed it into the chamber from the magazine. Then measure the shoulder length again. Your rifle might be bumping the shoulder during chambering.

I recently tested my AR10 and it is bumping the shoulder .004” from the mag and .007” if I just drop one in the chamber and let the bolt fly.

As a result of that test I now bump the shoulders .002” just like for my bolt gun.

So do you bump it back to a point you get 0 additional bump from chambering or to compensate for the additional bump it will get from being chambered?

 

[918v]

I bump .002” from the point of zero clearance.

I need minimal clearance for single feeding.

I am content with the fact my gun is going to bump the shoulder no matter what, but I’m not going to help it do that.

If I start with .004” shoulder bump my gun is going to add another .004”.

 

[2aBaC̶a̶]

I bump .002” from the point of zero clearance.

I need minimal clearance for single feeding.

I am content with the fact my gun is going to bump the shoulder no matter what, but I’m not going to help it do that.

If I start with .004” shoulder bump my gun is going to add another .004”.

Interesting, seems like in theory you could bump the shoulder back enough that you get 0 added bump on chambering. And that would be just under your actual Zero. I mean at some point the shoulder shouldnt hit in the chamber.

 

[Egonzalez3]

Load them to mag length.

With regard to shoulder length, don’t bump more than for a bolt gun. First find zero clearance length, then load a dummy round, and let the bolt feed it into the chamber from the magazine. Then measure the shoulder length again. Your rifle might be bumping the shoulder during chambering.

I recently tested my AR10 and it is bumping the shoulder .004” from the mag and .007” if I just drop one in the chamber and let the bolt fly.

As a result of that test I now bump the shoulders .002” just like for my bolt gun.

So

Load them to mag length.

With regard to shoulder length, don’t bump more than for a bolt gun. First find zero clearance length, then load a dummy round, and let the bolt feed it into the chamber from the magazine. Then measure the shoulder length again. Your rifle might be bumping the shoulder during chambering.

I recently tested my AR10 and it is bumping the shoulder .004” from the mag and .007” if I just drop one in the chamber and let the bolt fly.

As a result of that test I now bump the shoulders .002” just like for my bolt gun.

My main concern is seating depth. Currently sitting @ 2.941. Even if I bump it back .030, I will never get it to SAAMi spec. Therefore, my main concern is safety, and of course achieving accuracy. To your point, I should be more concern with fitting my magazine.

 

[2aBaC̶a̶]

Why are you at 2.941?

 

[918v]

Interesting, seems like in theory you could bump the shoulder back enough that you get 0 added bump on chambering. And that would be just under your actual Zero. I mean at some point the shoulder shouldnt hit in the chamber.

When I said zero clearance I meant between the back of the case and the bolt face and bolt lugs.

 

[918v]

So

My main concern is seating depth. Currently sitting @ 2.941. Even if I bump it back .030, I will never get it to SAAMi spec. Therefore, my main concern is safety, and of course achieving accuracy. To your point, I should be more concern with fitting my magazine.

Safety is not a concern when loading to mag length. There is nothing unsafe about it. What is so special about 2.941”?

 

[918v]

Why are you at 2.941?

Prolly because some retard told him that chasing lands is the way to go.

 

[Egonzalez3]

Prolly because some retard told him that chasing lands is the way to go.

Correct. Measured for lands with the hornady OAL gauge. C.O.A.L came to 2.941.

 

[2aBaC̶a̶]

Any chance HK throat those barrels long? I've never actually tried to find the lands on any of my ARs

You might run a seating test to see if it even matters. I almost always do book OAL making sure it fits in a mag. For reliability.

 

[Egonzalez3]

Any chance HK throat those barrels long? I've never actually tried to find the lands on any of my ARs

You might run a seating test to see if it even matters. I almost always do book OAL making sure it fits in a mag. For reliability.

That's a good question on the throat. At that length without measuring I can see it sits on the mag just a tad bit long. I understand the measurement provides a starting point, and my understanding is to start cutting back on C.O.A.L at least .030. I read somewhere in a forum where someone with the same AR had it .015 from the lands.
I measured an unfired factory remington 180 grain C.O.A.L and it measured 2.709. I noticed the spent cartridges had pressure marks. Thus, it tells me I have to get closer to the lands. Albeit, the brass I will be using are new Lapua palma brass, so along with Sierra TMK results will differ.

 

[NCHillbilly]

Don't mistake cartridge overall length (base to bullet tip) with length to the datum (about mid shoulder). They are two completely different measurements. If your rifle is mag fed, you are limited on your overall length to mag length, unless you want to single load. Headspace is measured from the base to the datum. Without a headspace comparator (about $40.00), you're just kinda guessing on your resizing die adjustment. If you follow the die manufacturer's instructions, you'll usually be in the ballpark, but with the comparator, you can dial it in a little better, which should improve brass life.

 

[918v]

That's a good question on the throat. At that length without measuring I can see it sits on the mag just a tad bit long. I understand the measurement provides a starting point, and my understanding is to start cutting back on C.O.A.L at least .030. I read somewhere in a forum where someone with the same AR had it .015 from the lands.
I measured an unfired factory remington 180 grain C.O.A.L and it measured 2.709. I noticed the spent cartridges had pressure marks. Thus, it tells me I have to get closer to the lands. Albeit, the brass I will be using are new Lapua palma brass, so along with Sierra TMK results will differ.

You control pressure by adjusting the powder charge, not by cartridge overall length.

 

[Egonzalez3]

Don't mistake cartridge overall length (base to bullet tip) with length to the datum (about mid shoulder). They are two completely different measurements. If your rifle is mag fed, you are limited on your overall length to mag length, unless you want to single load. Headspace is measured from the base to the datum. Without a headspace comparator (about $40.00), you're just kinda guessing on your resizing die adjustment. If you follow the die manufacturer's instructions, you'll usually be in the ballpark, but with the comparator, you can dial it in a little better, which should improve brass life.

I have a hornady bullet comparator, and from everything I have read your suppose to measure from the base to the ( bullet ) ogive to get the correct O.A.L. I understand base to datum is in part the sum of (2) parts. The other being datum to ogive - a fixed value according to bullet type. I am using new brass, and I understand reloading requires trial and error. I appreciate all the feedback / discussion.

 

[2aBaC̶a̶]

Finding your lands is a point of reference. You still need to experiment with what your rifle likes. There is no universally right number off the lands, -.02 is a generic rule of thumb. the only right number is the one that works best for your rifle and bullet combo.

The bullet comparator is supposed to reference the same point at which your lands engage the bullet. I use it, it works well and is a more accurate way to measure than base to tip.

 

[NCHillbilly]

I have a hornady bullet comparator, and from everything I have read your suppose to measure from the base to the ( bullet ) ogive to get the correct O.A.L. I understand base to datum is in part the sum of (2) parts. The other being datum to ogive - a fixed value according to bullet type. I am using new brass, and I understand reloading requires trial and error. I appreciate all the feedback / discussion.

The bullet comparator you have will allow you to get a consistent measurement for your bullet seating depth, but a headspace gauge allows you to measure from the cartridge base to the datum line. If you measure 3 cartridges that have been fired in your weapon, take the avg of those 3 and that will give you your weapon's headspace. Take that measurement and subtract .002"-.003". Set your sizing die to give you that measurement (assuming you're shooting a gas gun). If you're shooting a bolt gun, you can subtract .001"-.002". This is what is referred to as shoulder "bump".
As for the bullet comparator, I would pick 10 of the bullets that I plan to load, measure the bullet length, then load the longest of them to mag length. All bullets won't usually measure the same, even with polymer tips. Once you have a round loaded at mag length, then use the comparator to measure to the ogive. Using this measurement will give you a consistent number each time, assuming the quality control of the bullet manufacturer is up to snuff. Record all your measurements so that you'll have a quick reference later on.

 

[Snuby642]

Are you planing on single feeding?

 

[Snuby642]

Go back to the front of your reloading manual read the explinations for,
COAL, base to ogive, base to datum (shoulder).

You are confusing coal and base to ogive .
Ogive is going to hit lands, coal is going to hit magazine.

Imho

 

[Egonzalez3]

The bullet comparator you have will allow you to get a consistent measurement for your bullet seating depth, but a headspace gauge allows you to measure from the cartridge base to the datum line. If you measure 3 cartridges that have been fired in your weapon, take the avg of those 3 and that will give you your weapon's headspace. Take that measurement and subtract .002"-.003". Set your sizing die to give you that measurement (assuming you're shooting a gas gun). If you're shooting a bolt gun, you can subtract .001"-.002". This is what is referred to as shoulder "bump".
As for the bullet comparator, I would pick 10 of the bullets that I plan to load, measure the bullet length, then load the longest of them to mag length. All bullets won't usually measure the same, even with polymer tips. Once you have a round loaded at mag length, then use the comparator to measure to the ogive. Using this measurement will give you a consistent number each time, assuming the quality control of the bullet manufacturer is up to snuff. Record all your measurements so that you'll have a quick reference later on.

I am shooting with an AR10. Therefore, I have to get a headspace gauge to follow up with the spent cartridges. I am using new palma brass. I used Hornady OAL gauge and bullet comparator to achieve seating depth. However, your saying to concentrate on the magazine length.

 

[Snuby642]

Yes normally you will hit the magazine first hut still nice to know how much jump to the lands with different bullets.

 

[Egonzalez3]

Go back to the front of your reloading manual read the explinations for,
COAL, base to ogive, base to datum (shoulder).

You are confusing coal and base to ogive .
Ogive is going to hit lands, coal is going to hit magazine.

Imho

Understood. Those terms are equal whether your shooting bolt or gas guns.

 

[Egonzalez3]

Yes normally you will hit the magazine first hut still nice to know how much jump to the lands with different bullets.

Great, I already have a starting point to the lands. Will work on the magazine length.

 

[Egonzalez3]

Finding your lands is a point of reference. You still need to experiment with what your rifle likes. There is no universally right number off the lands, -.02 is a generic rule of thumb. the only right number is the one that works best for your rifle and bullet combo.

The bullet comparator is supposed to reference the same point at which your lands engage the bullet. I use it, it works well and is a more accurate way to measure than base to tip.

That has been the consensus on what I've read. I have seen any where from -.02 through -.030 as a starting point. The smaller value I feel are for more experienced loaders - I need to crawl before I can walk. I'm one to throw caution in the wind.
Thanks. All feedback has been great. Engaging with others with similiar interests provide great insight / learning opportunities.

 

[2aBaC̶a̶]

That has been the consensus on what I've read. I have seen any where from -.02 through -.030 as a starting point. The smaller value I feel are for more experienced loaders - I need to crawl before I can walk. I'm one to throw caution in the wind.

First of all it's an AR so its essential they fit and feed in a magazine. So yeah that is very important.

The main reason you want to know where your lands are is that jamming is bad and causes problems.

Keep in mind every bullet is different.
For example in my 6.5cm lands are at 2.2520 BTO using the hornady OAL tool and .264 comparator.
My rifles favorite factory ammo Hornady American gunner 140gr HPBT is loaded to 2.1960 @ .056 off lands.
My hand loads 140 ELD are 2.2260 @ .026 off.
I load Lehigh defense match solids and they barely fit in the mag at 2.800 overall which ends up being 2.1035 Base to Ogive and a whopping .148 off the lands.

All shoot great.

Find a load your gun likes and play with the seating depth last to fine tune the groups.

 

[918v]

I have a hornady bullet comparator, and from everything I have read your suppose to measure from the base to the ( bullet ) ogive to get the correct O.A.L. I understand base to datum is in part the sum of (2) parts. The other being datum to ogive - a fixed value according to bullet type. I am using new brass, and I understand reloading requires trial and error. I appreciate all the feedback / discussion.

In your case you don’t need to measure to the ogjive because you are miles away from the lands. You need to measure to the bullet tip so your rounds will fit in the mag.

 

[flyright]

After measuring many dozens of AR's - 10's and 15's, I've never found one that would even come close to touching lands with ANY bullet loaded to a mag fitting COAL. I've always been a proponent of starting at a comfortable max mag length and working shorter from there to find best accuracy - with attention paid to pressure signs, of course. Several times I've seen .04 to .12 under mag length provide best accuracy. Latest was a 6.5CM w/ 147 ELD and a .308 w/ 175 SMK that shot awesome with a COAL at 2.76. That would easily fit a PMag. Just my .02.

 

[918v]

I am shooting with an AR10. Therefore, I have to get a headspace gauge to follow up with the spent cartridges. I am using new palma brass. I used Hornady OAL gauge and bullet comparator to achieve seating depth. However, your saying to concentrate on the magazine length.

You don’t need a HS gauge. You need to take your longest case (shoulder length) and size it incrementally to see what your chamber will accept. Once you have the zero clearance length, you can then decide how much further to shorten it.

Gauges are not your chamber. Your chamber is your chamber.

 

[flyright]

I got away from sizing semi auto brass back .003-.004 a long time ago. I size it with the same die setup as my bolt guns - .0015 under and I've never had an issue. My SA chambers are all very close to my bolt gun chambers. I do not, however, let my gas guns go more than a couple hundred rounds before at least cleaning the chamber.

 

[Snuby642]

I got away from sizing semi auto brass back .003-.004 a long time ago. I size it with the same die setup as my bolt guns - .0015 under and I've never had an issue. My SA chambers are all very close to my bolt gun chambers. I do not, however, let my gas guns go more than a couple hundred rounds before at least cleaning the chamber.

A good point made.
If not using or lending ammo between guns and keeping a resonably clean
chamber it will run at 002 bump.

I had failure to chamber in cold weather with a dirty gun running 002 bump.
I ran it like a dirty pig in the heat no troubles.

I have went to 0035-004 bump and my ammo runs fine in five different ar's we own.

I belive the extra bump is for dirty chambers, high rate of fire, and interchangeability.

I have also started cleaning them more often. Lol