OAL vs bullet seating depth

willrussellville · October 3, 2010, 10:38 PM

I know this is probably not correct terminology but... please help me word this correctly and understand. When loading 9mm and going by the overall length listed in the reload manual, the bullet is seated so shallow that one has come out of the case when chambering. I have read that if you seat the bullet too far that it is very dangerous and causes excessive pressure so I am going slow and trying to learn. How important is OAL when it is shorter than specs and is there any published data on how far the bullet needs to be/may be seated into the brass? If I knew how far the bullet should be seated, I could measure and mark the bullet to set my die..

chris in va · October 4, 2010, 12:36 AM

Well, I'm no expert but have loaded a few thousand 9mm and 45 the past year, both FMJ and cast lead.

The reloading manuals will generally give a safe minimum loading depth, so I wouldn't worry about that. Really you're more concerned with feeding and chambering reliability than an exact OAL for that particular bullet shape and design.

For example, my CZ 75BD absolutely will NOT chamber my Lee 125gr flat nose bullets until 1.01oal...extremely short compared to a normal FMJ at 1.15. So to compensate I will charge at medium to minimum powder loads to be on the safe side.

On the other hand a too-long OAL can cause problems in the magazine. I had just started using my Lee 225 45acp mold and shoved it in to what I *thought* would chamber in my Sig. Turns out the bullet design was such that it would hang up in the magazine and not feed, so had to shorten it another .02 or so.

The other guys are a LOT more knowledgeable than I am, but if I were you, I'd just start with a minimum charge and work your way up, once you find a total OAL that works for your gun.

Jim243 · October 4, 2010, 02:22 AM

On 9mm I use a range of 1.090 to 1.150 OAL depending on the type or weight of bullet.

Jim

Replay13 · October 4, 2010, 03:51 AM

What bullet are you loading and at what OAL? If your in the reloading book specs the OAL is prolly ok.
I would look at neck tension, if your loading on a single stage press try not expanding the case and don't crimp it either.. just size the case and then seat the bullet. You can measure the case after sizing and then after bullet seating to make sure your sizing die is sizing the case enough.
I would suggest that you load a few dummy rounds and then cycle them through your pistol several times to see if the bullets have any setback or any comes out of the case.
Expanding and crimping just makes the bullets fit looser in the case strange as it may seem. You can verify this by making the dummy rounds and then see how many times you can cycle them through your pistol before you start getting any setback (or changes on OAL).
I load a lot of .40S&W and after a lot of testing I never expand or crimp... just size and prime and power then seat a bullet. Otherwise I would be getting some setback after just a few hard cycles in my XDM. Anyways measure the loaded round and then check for setback.
Also if your loading a really light short bullet not as much will be in the case and could cause your problem.
James

The_Stig · October 4, 2010, 05:25 AM

More information is needed to accurately assess your issue. What bullet weight and type will make a difference here. What OAL are you using? While it is true that seating a bullet too deep will alter the chamber pressure, there is a little freedom for adjustment.

Without further information, I would have to agree with Replay13 that neck tension may be the culprit. What type of crimp did you use? There are several other variables that affect neck tension. A little information about your seating and crimping procedure would be helpful.

October 3, 2010, 10:38 PM	#1
willrussellville Member Join Date: May 26, 2010 Location: Arkansas Posts: 78	OAL vs bullet seating depth I know this is probably not correct terminology but... please help me word this correctly and understand. When loading 9mm and going by the overall length listed in the reload manual, the bullet is seated so shallow that one has come out of the case when chambering. I have read that if you seat the bullet too far that it is very dangerous and causes excessive pressure so I am going slow and trying to learn. How important is OAL when it is shorter than specs and is there any published data on how far the bullet needs to be/may be seated into the brass? If I knew how far the bullet should be seated, I could measure and mark the bullet to set my die..

October 4, 2010, 12:36 AM	#2
chris in va Senior Member Join Date: December 26, 2004 Location: Louisville KY Posts: 13,806	Well, I'm no expert but have loaded a few thousand 9mm and 45 the past year, both FMJ and cast lead. The reloading manuals will generally give a safe minimum loading depth, so I wouldn't worry about that. Really you're more concerned with feeding and chambering reliability than an exact OAL for that particular bullet shape and design. For example, my CZ 75BD absolutely will NOT chamber my Lee 125gr flat nose bullets until 1.01oal...extremely short compared to a normal FMJ at 1.15. So to compensate I will charge at medium to minimum powder loads to be on the safe side. On the other hand a too-long OAL can cause problems in the magazine. I had just started using my Lee 225 45acp mold and shoved it in to what I thought would chamber in my Sig. Turns out the bullet design was such that it would hang up in the magazine and not feed, so had to shorten it another .02 or so. The other guys are a LOT more knowledgeable than I am, but if I were you, I'd just start with a minimum charge and work your way up, once you find a total OAL that works for your gun.

October 4, 2010, 02:22 AM	#3
Jim243 Senior Member Join Date: January 6, 2009 Location: Just off Route 66 Posts: 5,067	On 9mm I use a range of 1.090 to 1.150 OAL depending on the type or weight of bullet. Jim

October 4, 2010, 03:51 AM	#4
Replay13 Junior Member Join Date: April 26, 2010 Posts: 9	What bullet are you loading and at what OAL? If your in the reloading book specs the OAL is prolly ok. I would look at neck tension, if your loading on a single stage press try not expanding the case and don't crimp it either.. just size the case and then seat the bullet. You can measure the case after sizing and then after bullet seating to make sure your sizing die is sizing the case enough. I would suggest that you load a few dummy rounds and then cycle them through your pistol several times to see if the bullets have any setback or any comes out of the case. Expanding and crimping just makes the bullets fit looser in the case strange as it may seem. You can verify this by making the dummy rounds and then see how many times you can cycle them through your pistol before you start getting any setback (or changes on OAL). I load a lot of .40S&W and after a lot of testing I never expand or crimp... just size and prime and power then seat a bullet. Otherwise I would be getting some setback after just a few hard cycles in my XDM. Anyways measure the loaded round and then check for setback. Also if your loading a really light short bullet not as much will be in the case and could cause your problem. James

October 4, 2010, 05:25 AM	#5
The_Stig Junior Member Join Date: March 21, 2010 Posts: 7	More information is needed to accurately assess your issue. What bullet weight and type will make a difference here. What OAL are you using? While it is true that seating a bullet too deep will alter the chamber pressure, there is a little freedom for adjustment. Without further information, I would have to agree with Replay13 that neck tension may be the culprit. What type of crimp did you use? There are several other variables that affect neck tension. A little information about your seating and crimping procedure would be helpful.