Question on OAL and Xtreme Flat Point 9MM

[thefish]

I was going to order some more 9mm 124gr round nose from xtreme with the 10% off

I have done a load development with tightgroup and the recommended OAL (can recall what it is right now). 3.6gr in my shield cycles reliably.

If I switch to the flat point, I assume since the weight of the bullet and bearing surface is the same, I can use the same powder charge, but what about OAL? obviously the length of the bullet itself is shorted than a round nose, so that would lead me to believe that the OAL needs to be longer to have the same volume inside the case.

Sorry for the NOOB question. Thanks in advance.

 

[rcmodel]

No, the OAL will have to be shorter.

The FP is shorter than a RN of the same weight.

But there is going to be more full diameter bullet shank behind the ogive and less ogive.

So, you need to seat shorter to get most of the full diameter shank inside the case or it will jam into the rifling leade when chambering.

Take your barrel out of the gun and use it to do the Plunk test.
Just keep seating shorter until the round will fall into the chamber with a plunk, and fall out of it's own weight.

No need to concern yourself with internal volume as your 3.6 grains Titegroup is only a low pressure starting load.

rc

 

[thefish]

awesome, thanks for the detailed reply RCmodel.

As usual, I am grateful for the wealth of knowledge this forum has.

 

[RussellC]

RC answered that same question for me a while back. I just subtract the known length of the flat point from the length of the RN. OAl on the FP round will be reduced accordingly.

Russellc

 

[wlkjr]

I also use 3.6 Titegroup with a 124 gr. but use the Xtreme Hollow Point. I use an OAL of 1.120 but could go longer. This load shoots well and is plenty accurate out of my three 9mm Glocks. Also functions well with the Nano.

 

[LeftyTSGC]

FWIW, my 2 cents wrong or right, it works for me......If you want to make your head hurt and make it complicated try this,,,, Its not as simple as subtracting the round nose length from the FP lentgth. I seat a 9mm FMJ RN MG 124gr bullet at 1.130, I seat an Xtreme 124gr HP at 1.100 for the same barrel, it is based on the bullet Ogive distance from the barrel lands. My shell case base to Ogive is .883 that is set for all bulelts based for that specific barrel, then i can measure the remaing length and make that my OAL. Each bullet will be different but the .883 will never change based on the perfect shell length of a 9mm. the Overall length will be determined by the distance left after you have determined your Ogive to lands distance seated in the bullet. If you sit the bullets beside each other you will see that they do not all have the same distance from base to Ogive. You can achieve this by doing the "Plunk" test and taking a marker and determing where your lands touch the bullets, this distance is your true ogive to lands distance. Of course you may want to recess by .010-.030 if you want space for the bullet to jump, in my case by .020, so my base to ogive is .863 for all of my 9mm loads for that specific barrel.:banghead:

That is the easy complicated way: to get more exact, you need to measure using one piece of brass; because we know that a 9mm headspaces off of the case mouth so when you use the marker method you actually need to measure the distance from the case mouth to the mark on your bullet (ogive) that is the true distance for seating your bullet based on the casemouth which will be constant since the distance to lands is now a fixed point, that distance never changes in your barrel, so because we know that each piece of brass may be a different length, you would have to seat each bullet individually to get the exact distance everytime. So now you can reduce that by .010-.030 if you want bullet jump and find your depth. So, in theory this would make each bullet (if cases are not all the same length) OAL different if you want each bullet to be optimal. But because this would be to time consuming i would just use the first method above to get as close to perfect as possible without going crazy.:banghead::banghead: