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Durkin Tactical Franklin Armory
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Posted: 8/18/2017 9:29:50 PM EDT
I have a g20sf, to which i added a kkm 6 inch barrel and 22# wolff spring/steel rod.  It will fail to feed a couple times per mag with undewood 200 gr hardcast and underwood 200 gr xtp.  I have had no jams with 180 gr remington fmj and 165 gr underwood gold dots with the kkm or stock setup.  Should i expect jams with the 200 gr loads?  I avoided 220 gr hardcast because i knew they had a history of jams.
Link Posted: 8/19/2017 9:46:47 AM EDT
Return to stock barrel then try it. No don't believe the garbage talkers claiming your glock becomes a hand grenade with cast bullets in the OEM barrel. Might even try going back to the stock recoil spring as well
Link Posted: 8/19/2017 12:51:38 PM EDT
Yep...go back to stock recoil spring.
Link Posted: 8/19/2017 2:32:02 PM EDT
I installed a heavy tungsten rod/spring in my G40 because in intended to shoot only stout hard cast 10mm loads. So far no problems from 220gr HC down to 115gr Defenders. The glock store doesn't the list the spring tension weight only the weight of the unit. Never shot it with the stock rod/spring, but I shoot hard cast ammo through the stock barrel and a 7" KKM Precision barrel. No issues. Hope you figure it out.

Chrono results from this morning. ProChrono @ 10", 5 shot avg. 83 deg F.

Glock G40 10mm stock 6" barrel.
Underwood 10mm 200gr HC FP = 1224fps, 665ft.lbs (Advertised 1250fps)
Underwood 10mm 220gr HC FP = 1191fps, 693ft.lbs (Advertised 1200fps)

Glock G40 10mm w/ 7" (seven)KKM Precision barrel.
Underwood 10mm 200gr HC FP = 1253fps, 697ft.lbs
Underwood 10mm 220gr HC FP = 1248fps, 761ft.lbs
Link Posted: 8/19/2017 4:21:51 PM EDT
Back to stock barrel and spring.  Maybe there are differences magazine to magazine?  Didn't think to swap mags before i ran out of ammo.
Link Posted: 8/21/2017 8:59:43 PM EDT
I shoot COATED 200gn & 220gn HC loads through the stock tube of my G40 with no issues.

This includes factory ammo (BB & DT) and my own hot handloads.  Accuracy is excellent.  The poly coating aids in feed-reliability as well as in not gunking-up the barrel with lead residue.
Link Posted: 8/23/2017 1:39:06 PM EDT
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Back to stock barrel and spring.  Maybe there are differences magazine to magazine?  Didn't think to swap mags before i ran out of ammo.
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Curious to hear about your results.
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