View Full Version : Bullet Seating Depth for .45 ACP

January 30, 2011, 06:56 PM
So this is the first question I've posted as I'm a new member. This is also the first batch of ammo that I have reloaded so I am as green as they get. My problem is that I am trying to determine the proper bullet seating depth for my ammo. I am reloading winchester brass with an overall length of 0.898" and I am using Hornady 185 grain XTP's. I used 8.7 grains of SR-4756 and Winchester WLP primers. When I was done, if I remember right the maximum overall length was 1.275"? I measured some storebought ACP I had nearby and copied it seating my bullets with an overall length of 1.245. I was looking in a thread here where someone recommended removing the barrel and dropping the rounds in to see if they were headspaced correctly. I tried it and noticed that my rounds were getting slightly stuck. They weren't easy to pull out of the barrel like the factory rounds were. This led me to believe that the bullets were sticking out too far and were wedging into the rifling in my barrel. I assumed that I had made a mistake because I was using 185 grain hp's and the loads I copied were 230 grain target rounds. I found some hollowpoints I had Remington Golden Sabers and Hornady critical defenses. They were much shorter. I reseated the bullets deeper until they slid in and out easily and appeared to be headspacing properly. I now have lots of 10 rounds in increments from 1.225" to 1.21". I am a little concerned because that is a full five tenths of an inch less than the max oa length and I'm wondering if pressure may build up too quickly. I really don't want to blow my fingers off and ruin my xdm on my first batch so I could certainly use some guidance. What are your opinions?

January 30, 2011, 07:35 PM
This thread explains determining max OAL - http://www.thehighroad.org/showthread.php?t=506678

Of course, once you determined the max OAL, then you should determine the best "operating" OAL by incrementally decreasing the OAL and feeding/chambering from the magazine by manually releasing the slide.

Longest OAL that will feed/chamber reliably from the magazine will produce more consistent chamber pressure (as bullet will engage the rifling sooner) and more accurate shot groups.

If you shoot lead bullets, longer OAL will help reduce gas cutting and bullet base erosion, which will reduce leading in the barrel at the chamber end.

January 30, 2011, 10:22 PM
Based on my old Hornady data, FYI:

SR-4756 is typically selected for the hottest loads.
Your 8.7-gr of SR-4756 is only 2.25% off the maximum of 8.9! (IMR data recommends a starting load of 7.4-gr of SR-4756 with a max of 8.2-gr for a 185-gr HDY JSWC.)
Hornady's recommended cartridge overall length (OAL) is 1.230-inch, not something you copied from an similar cartridge.
Your concern about over pressure loads is well founded.

About your bullets becoming slightly stuck, I suspect it's due to the bell not being fully eliminated and you getting friction in the chamber. The "straight walled" .45ACP case is actually tapered about 0.003-inch. IMHO, your bullet isn't engaging the rifling with your 1.225-inch OAL. Hopefully you are using separate seating and crimp dies. Many newbies get into trouble using a combination seat and crimp die -- it very easy to mess up the adjustment. Set you seating die high enough so it doesn't start to crimp and then adjust the seating depth with the ram's screw. Then crimp with a separate die. (I set my crimper to give me .470-inch at the case mouth.) Instead of guessing, you might want to get a cartridge gauge and a set of calipers.

May I suggest a bullet puller for your existing hot loads, and start over with your seater set for a COL of 1.230-inch, a crimp die set to remove the bell, and a milder start-up load.

Good luck and be safe.

January 30, 2011, 11:53 PM
OK, I'm also very new at this, so don't take my advice as gospel.

The .45 ACP headspaces on the case mouth. This means that when you drop a cartridge in the chamber there is a light step in the chamber, and the case mouth rests on that step.

If you don't seat your bullets so that the shoulder of the bullet is flush with the case mouth, that lip in the chamber may bite into the lead shoulder of the bullet and/or lube stuck on that shoulder.

See the left-most bullet here:


The left-most bullet was where I tried to seat the bullet per OAL of another bullet, and found, of course, that my Oregon Trail Laser-cast bullets needed to be seated a bit deeper in order to make the shoulder of the bullet flush with the case mouth, which I did on all subsequent rounds.

From what I have gathered, OAL is not that important. Yes, you need to be within the specifications you find in reload handbooks, and yes you don't want to over-compress the bullet as this can cause dangerous overpressures.

But I suspect that any bullet designed for 45 ACP will also be designed so that it's shoulder sits at least flush with the case mouth. Otherwise the shoulder of the bullet will dig into the lip in the chamber.

They say a good way to test your cartridges in your chamber is to drop them in and see if you can spin the cartridge. If it spins freely, you've got a good case mouth seating. If it sticks, you might be sitting on the bullet shoulder. (Or you might have lube on your cases, or your crimp size may be wrong)


chris in va
January 31, 2011, 12:11 AM
My Lyman manual shows a 185gr SWC with 4756 at 5.7 to 7.7gr max. Sounds like you have quite the +P load going there!

No info with a 185gr JHP, but the 200gr JHP has 5.4 to 7.4 max.

January 31, 2011, 01:59 AM
Manbearpig, That's one hell of a combination.

You are ok on the powder load of 8.7 grains of SR 4756 a mid-range load at about 950 FPS. But your OAL should be 1.225 for that bullet (Hornady HP-XTP 185 grain #45100). The min charge is 8.2 grains and the max charge is 9.1 of SR 4756.

Buy the book "Hornady Handbook of Cartridge Reloading 8th edition".


PS: the 45 ACP is now called the 45 Automatic

January 31, 2011, 05:40 AM

Steve, you're applying what works for you with a cast bullet with a shoulder to a jacketed bullet that doesn't. I use the same method you do with cast bullets. With jacketed, I tend to go with what the maker recommends.

January 31, 2011, 07:22 AM
Your manual does a pretty good job of giving you the proper seating depth. But it's expressed in over all length of the cartridge with bullet seated.

230 gr. Hardball would, for example, run from 1.255 to 1.270 max., with Remington hardball being 1.262 being OAL (overall length) last time I measured some. Nose shapes aren't the same so OAL's will vary a little. It can also be expresses as COL (cartridge overall length) or sometimes LOA (length overall)--all the same thing.

230 gr. JHP's would be seated down in the case to the approximate same depth as hardball, but because of the shorter nose, the loaded round would have a shorter OAL. For example, 230 gr. HST is 1.215.

Semi wacutter ammo is seated so a little shoulder is showing and OAL would be, typically, from 1.250 to 1.260. No doubt there are those who'll chime in and say they seat theirs to 1.245 or what ever. Make sure some shoulder is showing on SWC's. At least the thickness of two business cards.

Since the loaded rounds must fit the magazine, 1.270 is listed as max in all the manuals I have, but not all bullets fit all magazines when seated to max.

Summary: REFERRING TO MANUAL WORKS QUITE WELL FOR DIFFERENT BULLETS. They give OAL for their test loads they test, and some manuals, like Lymans gives data for cast bullets.:cool:

Beginners lesson concluded: ;)

January 31, 2011, 10:35 AM
Steve, you're applying what works for you with a cast bullet with a shoulder to a jacketed bullet that doesn't. I use the same method you do with cast bullets. With jacketed, I tend to go with what the maker recommends.

I hadn't thought of that. I see from the pictures on MidwayUSA that jacketed bullets tend to have smooth sides.


January 31, 2011, 12:01 PM
Headspacing cast and swaged bullets on the bullet improves their accuracy. I've not found it does anything for jacketed bullets. They tend to be tough enough to center themselves on the way into the throat at .45 ACP pressures, where the lead bullet can swage in at an angle.

To the OP: Pressure can change dramatically with seating depth. Seating depth is how far the base of the bullet sticks into the case. I affects how much volume the powder starts burning in, and the smaller that is, the faster the powder gets burning, which raises pressure if the primer hasn't unseated the bullet. This means that even for two bullets that are the same weight, if they have different lengths they will not make the same pressure with the same cartridge overall length (COL). Indeed, you may not even be able to use the same load with them.

Seating Depth = case length + bullet length - COL

For your XTP, especially as you are new at this, I recommend you use Hornady's recommended seating depth and their load data. They will have the most experience with it. Not only is their shape a little different from others, their particular jacket thickness and OD will affect pressure, too. Bullets, even of the same weight, cannot be counted upon to be interchangeable. Their load is:

185 grain XTP, Hornady case, Winchester WLP primer:

COL: 1.230"
SR4756: 7.8 grains starting load, 9.7 grains maximum.

Start with the starting load, not the middle of the range. Work up in steps of 0.3 grains while watching for pressure signs (http://www.shootersforum.com/showthread.htm?t=58763). Twice I've had manual starting loads turn out to be maximum in the gun I was using. Once another board member had a load just over half way up the range in the Speer manual turn out to be at proof pressure of around 75.000 psi in his gun. Every gun is individual so start low and work up.

Regarding cartridge fit in your gun: If you don't have a caliper get one. Harbor Freight always has inexpensive digital calipers (http://www.harborfreight.com/6-inch-digital-caliper-47257.html) that are good enough for reloading (get the steel and not their composite one). Midway has a sale on a Hornady branded one (http://www.midwayusa.com/viewproduct/?productnumber=417494) this month for the same price, but it's on backorder. With the calibper, measure the diameter of your cartridges at the case mouths of your finished rounds. Adjust your crimp die until they are 0.469" across.

There occasionally exist some lots of some brands of brass that have such thick necks they cannot be loaded to that specification without excessive crimping force. I recommend you use Starline or Winchester brass to avoid problems while you learn to reload. Play with mixed cases later when you are more familiar with what your a doing.

If you still can't get the rounds to fit, get a Lee carbide factory crimp die (http://www.midwayusa.com/viewproduct/?productnumber=716704) and run them through that. It sizes down the OD.


I know, I know. But the change doesn't seem to have taken. Run a search on ".45 ACP" at Midway and you get back 13 pages of about everything you can imagine with that name included. Run a search of ".45 Automatic" and you get back 13 pages of stuff that says ".45 ACP". Besides, I've got too many gun barrels and too many case headstamps with .45 ACP on them to give up now. ;)

January 31, 2011, 05:05 PM
Book OAL is only a suggestion, if your cartridges are feeding and chambering smoothly they are 'right.'

Most of the concerns about not seating too deep center on the 9mm. It's a small case using very fast burning powders at high - for a handgun - pressures to start with. Decreasing the 9 mm burn space make a MUCH larger difference than it does on most other cartridges, including the .45 ACP.

I suggest you fire a couple rounds and see if things don't work fine before worrying a lot more about it.

January 31, 2011, 11:15 PM

I don't understand it either, only thing I can think of is that after 100 years everyone got tired of giving Colt Pistol free advertising. Besides ACP is cooler than Automatic and easier to type.


February 2, 2011, 01:03 PM

Odd to single out the .45 ACP for redesignation. I wondered if they just thought three words were too many where one would do, but .45 Colt was already taken. If so, watch out for the .45 GAP to become .45 Glock.


.45 ACP is subject to the same laws of reduced % powder space creating a pressure increase that the 9 mm is. I did a calculation in QuickLOAD long ago that came out as illustrated below. When I finally got a pressure test barrel rigged up for .45 ACP, though, I found interesting irregularities from the predictions. It seems that with its small case volume under the bullet and the large bullet base area, a large pistol primer is often able to unseat the bullet before the powder gets very far into burning. Especially with lubricated lead bullets. The result is the powder getting up to start pressure in a bigger volume than the loaded cartridge had. The deeper the bullet was seated and the slower the powder, the more likely this was to happen. I just hate to suggest people count on working out that way.

The book COL for the Hornady bullet is a good starting point because Hornady also makes commercial ammunition with that bullet. So their established seating depth with it should be compatible in most guns. If it doesn't feed, obviously you may need to try adjusting it, but that doesn't mean the powder charge maximum will invariably be unaffected by making that change. Prudence suggests going to a modest target load for that experimentation, then working the charge up after the new seating depth is established.


February 2, 2011, 02:22 PM
watch out for the .45 GAP to become .45 Glock.
Or, perhaps, the .45 Glomatic.

Interestingly, I noted in my old NRA book, HANDLOADING, in the HANDGUN RELOADING DATA section, it refers to the cartridge as the .45 ACP, but in the REFERENCE SECTION it's called the .45 Automatic.

February 2, 2011, 07:48 PM
A lot of folks used to refer to the 1911 as a ".45 Automatic". The growth in popularity of non-bullseye competitions got more folks conscious of the original designation. I think what Jim is referring to is how SAAMI refers to the cartridge (http://www.saami.org/PubResources/CC_Drawings/C%20and%20C%20Dwgs%20-%20TOC%20-%20Pistol.pdf), which is .45 Automatic. We could probably write and ask what brought that about. But I just had supper and am feeling too lazy.

February 3, 2011, 12:25 AM
Book OAL is only a suggestion, if your cartridges are feeding and chambering smoothly they are 'right.'

Good grief.:(

In the illustration above, the round on the right would likely feed in most pistols and, as you can see, generates excessive pressures with a light TARGET load.

The .40 S&W is even more sensitive to excessive seating depth. I'd lose the " if your cartridges are feeding and chambering smoothly they are 'right.' philosophy.

Now, I suspect you didn't really mean it that way, but I wanted to make a point that seating depth can be excessive and cause problems. As far as the illustration is concerned, SWC's of that type are ALWAYS seated so a little bit of the shoulder is showing and therefore, one wouldn't need to worry about seating depth being excessive.

As for manuals giving recommended seating depths---I think it's more of a matter of telling you what they used to test their loads, and that there can be some variation.

February 8, 2011, 08:42 PM
Thanks for all the responses and advice everyone. After reading all your input I have decided to pull the bullets and start over.

Hopefully you are using separate seating and crimp dies. Many newbies get into trouble using a combination seat and crimp die -- it very easy to mess up the adjustment.
You were exactly right. I bought the Hornady 3 die set. I have a Lee Carbide 4 die set in the mail on its way right now. The seperate crimp die should hopefully eliminate the thick case mouths once I get it adjusted properly.

Buy the book "Hornady Handbook of Cartridge Reloading 8th edition".
I had the 7th edition which came with my lock n load kit. The 8th edition is also on it's way.

Start with the starting load, not the middle of the range. Work up in steps of 0.3 grains while watching for pressure signs.
As I have never done it before I assumed starting in the middle of a suggested range would be the safest. Thankfully you gave me this advice before I started firing away on my middle range charges. While I assume my gun would easily handle these loads, I suppose it's better safe than sorry, particularly where my fingers are concerned.

Thanks again everybody. I think this was just the advice I needed.