OAL Questions?

[Archer3267]

Hello Everyone

I am new to the board, new to reloading and new to owning a CZ Pistol (75B). I have been reading on this site & other sites about how to figure out the OAL of a cartridge in a pistol. I put one of the bullets I have to be used for reloading into a case. I then put it into the chamber until it fit with the bullet shoulder touching the rifling. I then took a black magic marker & colored the shoulder of the bullet & slowly moved it farther from the rifling until the black stopped being rubbed off the shoulder which gave me an OAL of 1.020" (1.025" OAL touching the rifling) using a 124 gr JHP Montana Gold Bullet in a Winchester case trimmed to 0.744". I know that CZ pistols historically have very short chambers but I am worried that this OAL is too short & also that it might not be far enough from the rifling. I also worry that I might have problems with FTF with a cartridge this short. I also noticed in reading other literature on reloading of the 9MM that some of the OAL's listed are as short as 1.010" but those are typically in the 90-100 gr loadings & I do not know if this matters. I am planning to use Universal Clays powder as this is the type of powder I have on hand. My Speer reloading manual states to use a starting charge of 4.5 grs of Universal behind a 124gr JHP. So my questions are is a OAL of 1.020" too short, and if not should I back off on the starting charge or should I use another type of bullet and or powder? Thanks in advance for any and all help you can provide me.

[High Lord Gomer]

Wow! I don't know anything about the CZs but that seems awful short.

What kind/weight of bullet are you using?

Will your CZ shoot WWB ammo? That stuff is loaded much longer than that.

[JoshF]

Your method is sound and I've done a similar test but I think you're being too critical on the marks. I typically take the barrel out of the gun then push a round in the chamber and while pushing see if it will spin at all. If the bullet engages the rifling trust me you'll KNOW. Otherwise it should still turn with little effort as just the case shoulder will be rubbing. I tested this in all the 9mms I had to come up with a OAL that works in all. It turned out that the Tanfoglio (CZ cloneish) I had at the time was the shortest chamber. At the time I ran MG 124 CMJ and anything over 1.140 would engage the rifling. I gave myself a little cushion and came down to the 1.130 I still use today. I'd say do the test again and make sure you are feeling definitive engagement on the rifling and not just a small rub that could be from the round having some play in the chamber. Let us know what you find.

[alellis]

I won't go into the load data since I have never used either JHPs or universal clays.

I will say however that my Shadow functions quite happily with 124g flat point at 1.08 oal

al

[DogmaDog]

Wow. My recommendations:

Stop trimming pistol cases.

Load a little (.005" to .01") shorter than published max length. Ensure the rounds will fit in a magazine.

Start at the starting load and work up in 0.2 gr. increments. Stop if you see signs of excessive pressure, or when you reach your desired power factor.

I have a hard time believing the CZ-75b's chamber is unusual. I have one, and I shoot lots of factory stuff through it. It works fine.

DD

[Archer3267]

Hello Everybody,

I remeasured again like I did before except I used 10 different cartridges this time of the same manufacture this. I removed the barrel left the cartridges long put them into the chamber and pushed them until they were seated properly. I then spun them to make sure they were not engaged in the rifling. My measurements were 1 @ 1.083", 2 @ 1.086", 1 @ 1.087", 2 @ 1.088", 3 @ 1.090" & 1 @ 1.092" for an average of 1.088". I have shot WWB 115 gr FMJ, Winchester Ranger 147 gr SXT & and other reloads which were 115 gr FMJ with no problems. So is this satisfactory or do I have a problem with to short of OAL. Thanks for your help & patience with a newbie to reloading.

[alellis]

Hello Everybody,

I remeasured again like I did before except I used 10 different cartridges this time of the same manufacture this. I removed the barrel left the cartridges long put them into the chamber and pushed them until they were seated properly. I then spun them to make sure they were not engaged in the rifling. My measurements were 1 @ 1.083", 2 @ 1.086", 1 @ 1.087", 2 @ 1.088", 3 @ 1.090" & 1 @ 1.092" for an average of 1.088". I have shot WWB 115 gr FMJ, Winchester Ranger 147 gr SXT & and other reloads which were 115 gr FMJ with no problems. So is this satisfactory or do I have a problem with to short of OAL. Thanks for your help & patience with a newbie to reloading.

So as I said 1.08 will work fine.

You can get along with longer oal with a different bullet profile. RN can be longer and still function ok also some factory is more pointed and still chambers ok.

Its good to remember that it is not the oal that is the be all and end all of either, whether the round will chamber or the power factor generated.

Different bullet profiles can be loaded to different lengths and still function.

The same weight bullets of different profiles can be loaded to different oal and still give the same PF

al

[High Lord Gomer]

You stll didn't mention the type of bullet you are using. The profile of a bullet can have more impact on when it reaches the rifling than the OAL.

Did you measure the OAL of those factory rounds? Unless you're loading wadcutters, I' surprised that a 1.16 OAL factory bullet would work but that you need to load to 1.08 to chamber properly.

[Archer3267]

Mike,

No problem I thought I covered that in my first post, but I am using Montana Gold 124 gr JHP in a Winchester case using WSP primers and Universal Clay powder.

[chirpy]

I always test a new SA with factory ball ammo first. This gives me a starting point with the weight bullet I'm looking to use. I then use one of the rounds to set my starting OAL. Since all RN bullets are not the exact same profile I load 50 rounds with a starting load and go to the range to function check this ammo. If it works 100% I load and save a dummy round for future setting of OAL (just in case). After that I do load development until I find an accurate load. When I run out of that bullet I use my dummy round to set things up to begin testing the new bullet and make adjustments if necessary etc., etc.

Works for me but maybe not for everyone...

Richard

[High Lord Gomer]

Mike,

No problem I thought I covered that in my first post, but I am using Montana Gold 124 gr JHP in a Winchester case using WSP primers and Universal Clay powder.

You did...I missed it. I do applaud your tact, it fits in perfectly here. If I had made that mistake on some other sites, I wouldn't have gotten such a nice response.

Sorry I can't help other than to mention what you probably already know; hollow points generally get loaded to shorter OALs because their lack of a point.