LiveLife
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jim000711, keyholing usually occurs due to improper bullet-to-barrel fit, especially for oversized factory barrels, that allows a lot of high pressure gas leakage around the bullet when the powder ignites that won't deform the bullet base (obturation). Instead of bullet base expanding to seal with the barrel and rotating with the rifling as the bullet travels down the barrel, the bullet skids down the barrel with insufficient rotation to stabilize the bullet in flight, causing sideways holes on target you described.jim000711 said:Trying to develop a load for Missouri 125 SWC lead ... and experienced "keyholing" or "tumbling."
For .356" diameter MBC 125 gr SWC lead bullet, your barrel should be .355" groove-to-groove. If your barrel is oversized (say .356"-.357"+), you may need to use larger sized bullets.
Keep in mind that 125 gr SWC bullet has substantial bullet base (see picture below) and will seat much deeper in the case neck than RN bullet (Due to this reason, I used .2-.3 gr below max load data of W231/HP-38 during my powder work up). With start-to-mid range load data of W231/HP-38, the 125 gr SWC load hardly showed any lube smoke out of .355" groove diameter Lone Wolf conversion barrels in G22/G27, indicating very good seal with the barrel with almost no gas leakage. I frequently produce 1" shot groups at 15 yards off hand with this load, even with the short barreled G27 and LW conversion barrel.
Slug your barrel and see what the groove diameter of the barrels are.