Round Nose and Conical Nose Load Question


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no_agenda
April 7, 2010, 07:56 AM
I am looking to load a 9mm 125gr LRN, but the hodgdon manual only gives data for a 124gr LCN, is it ok to load to a LRN to the specs of a LCN? Sorry for the newb question....just starting to reload:uhoh:

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loadedround
April 7, 2010, 11:22 AM
You can load any similar style lead bullet of the same weight with the same listed charge. Do not substitute a lead bullet for a jacketed one or vice versa...those charge weights will differ. BTW do not exceed OAL with either style bullet for proper fuctioning.

SlamFire1
April 7, 2010, 12:05 PM
Won't be a problem.

rcmodel
April 7, 2010, 01:21 PM
I disagree slightly.

A RN of equal weight to a TC or LCN bullet will be shorter.

Seating OAL will be about .050" shorter with the RN bullet to get the same amount of bullet shank inside the case.

Put another way, the max powder charge weight will be slightly less with the RN bullet because there is more full diameter bullet shank in contact with the bore which = more friction.

You can use the Hodgdon data, but not the seating depth listed for the LCN bullet.

rc

Steve C
April 7, 2010, 05:44 PM
As in all situations when hand loading and assembling rounds for the first time with new or different components, use a start load and work up watching for pressure signs. If only one load is listed and it doesn't have a notation that says "do not reduce" the the load is a maximum load and needs to be reduced by 10% for your start load.

Often the start load is quite satisfactory.

no_agenda
April 7, 2010, 05:53 PM
RC-Then how or where can i find OAL data of the differing LRN from the LCN listed in the hodgden manual?

orrwdd
April 7, 2010, 06:02 PM
RC-Then how or where can i find OAL data of the differing LRN from the LCN listed in the hodgden manual?
Lyman Manual #49 has reloading data for a 9mm conical bullet that you can use. It is based on a Lyman 125gr cast bullet.

Bill

rcmodel
April 7, 2010, 06:05 PM
Lyman #49 lists both RN and TC 120 grain cast bullets.
They would be very nearly 125's after the grease groove is filled.
They show 1.065" for the RN and 1.110" for the TC.

But even then, the Lyman bullet molds will probably not be an exact match for the Magma mold bevel-base designs most commercial casters use.

In general, you need to determing the OAL using the barrel out of your gun to chamber check the bullets you have.

Seat just deep enough to clear the rifling and drop fully & freely in the chamber, while also covering all the grease grooves and you should be good to go.

Whatever the OAL turns out to be, is what it is.

rc

helg
April 7, 2010, 06:27 PM
The attached puctire shows two 125gr 9mm bullets: of TCN and RN designs next to 9mm round that is loaded with the TCN bullet.

Lengths of the two bullets are almost identical: .587" for RN vs .591" for TCN. This difference should not affect internal ballistics when both bullets are loaded to the same OAL.

Important difference between the bullets is bearing surface length. It is .31" for TCN vs .24" for RN. The pictured TCN bullet has to be seated .07" deeper to cover lube grooves to the same level, like shown at the picture. The .07" is big difference. When bullet is seated deeper, powder charge should be reduced. QuickLoad indicates that the charge for the properly (i.e. deeper) seated TCN should be dropped significantly - from 3.56 to 3.06 grains on 700x to have the TCN bullet with the same chamber pressure.

fecmech
April 8, 2010, 08:50 PM
RC other than the Lyman TC most other tc's (lee, rcbs) will load shorter than the RN. The lee 121 TC loads at 1.048 which gives the same amount in the case and same bearing surface as the Lyman TC. The Lyman bullet is a long "pointy" TC. Most truncated cones are designed to be seated into the case at the transition point between the bearing area and the truncated cone.

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