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Old 04-20-2017, 01:17 PM
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What effect does reducing the bullet weight (of similar type) by a small amount have on pressure and velocity? For example, if I have some 150 grain LRN for .38 special, and I use load data for 158 grain LRN, what effect should I expect? My limited understanding leads me to believe that the velocity should increase slightly, and the pressure should decrease slightly. Is this generally the case, or am I missing something?
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Old 04-20-2017, 01:25 PM
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With identical powder charge, you won't see much increase in vel but you will have less pressures. Rule of thumb when you don't have data for a given bullet wt; it is always safe to use heavier bullet data for a lighter bullet of the same mat'l.
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Old 04-20-2017, 01:26 PM
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As long as you understand that is a "general" statement, you are correct. You can "generally" use load data for a heavier bullet safely.
Bullet profile, cast vs FMJ, seating depth, among other things can turn being generally correct to being specifically dangerous.
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Old 04-20-2017, 01:27 PM
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The velocity will increase or decrease depending on the bearing length of the driving bands from one bullet to the other. Longer driving band may increase pressure but not a lot. Larger diameter will increase pressure also but 8 grains. in weight shouldn't make a lot of difference. Best to reduce your charge a little and work your way back up.
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Old 04-20-2017, 01:28 PM
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Default The heavier the bullet is......

The heavier the bullet is, the less powder is used.

So shooting a 150 grain bullet with 158 grain data, any adjustment would be an increase in powder. Not making any adjustment would be safe and you could work up the load from there.

If shooting a 158 grain bullet with 150 grain data, any adjustment would be a decrease in powder. Knock off a couple tenths of a grain and work your way back up.

I usually ignore plus or minus 5 grains in the bullet weight. If the load is not near max I might ignore that altogether.
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Old 04-20-2017, 02:14 PM
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Originally Posted by Mr_Flintstone View Post
What effect does reducing the bullet weight (of similar type) by a small amount have on pressure and velocity? For example, if I have some 150 grain LRN for .38 special, and I use load data for 158 grain LRN, what effect should I expect? My limited understanding leads me to believe that the velocity should increase slightly, and the pressure should decrease slightly. Is this generally the case, or am I missing something?
Your general understanding is correct. As,said, when load data is not available for a bullet weight use data from the closest heavier bullet. In this case with only an 8gr difference or about 5% you will see little to no difference.
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Old 04-20-2017, 09:57 PM
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Your general understanding is correct. As,said, when load data is not available for a bullet weight use data from the closest heavier bullet. In this case with only an 8gr difference or about 5% you will see little to no difference.
Well said, and you used about half as many words as I did but got the point across. Sometimes I think I just say too much.
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Old 04-20-2017, 10:57 PM
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Originally Posted by Bugkiller99 View Post
As long as you understand that is a "general" statement, you are correct. You can "generally" use load data for a heavier bullet safely.
Bullet profile, cast vs FMJ, seating depth, among other things can turn being generally correct to being specifically dangerous.
The caveat was like mat'l/composition. Yes a 45/200gr lrn is diff than a 200gr jhp.
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Old 04-21-2017, 08:51 AM
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Thanks for the replies guys. The reason I asked is that I was going to make up some 200 grain .38 special super-police rounds, but my order for the 200 grain LRN bullets was cancelled due to a mix-up. When I tried again, they were out of stock, and all I could find was 190 grain LFP from Midway. I couldn't find load data for 190 grain, but Lee has data for 200 grain lead, and Lyman has data for 195 grain LRN. I figure data from either should be good for 190 grain LFP. There might be a slight difference in overall length due to the different point styles, but if I seat in the cannelure I should be OK shouldn't I?
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Old 04-21-2017, 12:20 PM
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Quote:
Mr. Flintstone wrote:
...if I seat in the cannelure I should be OK shouldn't I?
Using 200 grain lead bullet data with 190 grain lead bullets of the same diameter, composition and construction, you are probably going to be okay.

But note that it is not only bullet weight but composition and configuration that impact velocity and pressure. Two examples:
  1. If the lead in your bullets is made from a different, harder alloy than the bullets used to devleop the test data, it will take a higher level of pressure to get the bullet to engage with the rifling.
  2. If the bullet you are shooting has a hollow base then the propellant gasses will fill the hollow pushing its margins into contact with the rifling making it harder to move and thus requiring more pressure. If the bullets used to develop the load data had a flat base, they would not require as much pressure.

Begin with the starting load in your load data. Be alert to whether anything sounds or feels "off" when you shoot them and inspect the cases after firing for signs of pressure and then work up as indicated.
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Old 04-21-2017, 12:37 PM
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Seating depth is important.
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Old 04-21-2017, 01:53 PM
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Seating depth is important.
Yes & no. OAL in small volume pistol rounds, like 9mm & 40, with fast powders, like faster than W231, can be problematic. In the larger revolver cases with medium to slow burning powders, OAL just isn't moving the pressure needle much, especially if not loading to max. Of course something like a 148gr WC is NOT the same as a 150gr SWC, but in general, the heavy bullet data for lighter bullets works fine & OAL doesn't affect much. Load to the crimp groove. If the OP is using 200gr LRN data for a 190gr LFP, as long as he isn't starting at max, he should be fine.
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Old 04-21-2017, 03:37 PM
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Yes & no. OAL in small volume pistol rounds, like 9mm & 40, with fast powders, like faster than W231, can be problematic. In the larger revolver cases with medium to slow burning powders, OAL just isn't moving the pressure needle much, especially if not loading to max. Of course something like a 148gr WC is NOT the same as a 150gr SWC, but in general, the heavy bullet data for lighter bullets works fine & OAL doesn't affect much. Load to the crimp groove. If the OP is using 200gr LRN data for a 190gr LFP, as long as he isn't starting at max, he should be fine.
What you say about 9mm OAL is true however I would say the same analogy applies to using 190 grain or 200 grain bullets in 38 special. With a 190 grain bullet you will have as much of the bullet in the case as you would with a wadcutter fully seated and maybe even more. Using 200 grain data should be fine. I would expect pressures to increase much faster going up in charges weights than they would for your average 38 special load.
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Old 04-21-2017, 04:57 PM
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Default Just my two cents worth......

Cartridges based on those from black powder days, mainly rimmed revolver cartridges are MUCH less sensitive to deeper bullet seating than the rounds designed for semis that have small case volume and were designed for smokeless powder from the start. Pushing a bullet a little deeper in one of those will spike pressure dramatically.

.38 special (and subsequently the .357 magnum) .45 Colt and similar were all designed with black powder in mind.
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Old 04-21-2017, 05:28 PM
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What you say about 9mm OAL is true however I would say the same analogy applies to using 190 grain or 200 grain bullets in 38 special. With a 190 grain bullet you will have as much of the bullet in the case as you would with a wadcutter fully seated and maybe even more. Using 200 grain data should be fine. I would expect pressures to increase much faster going up in charges weights than they would for your average 38 special load.
Again, 200gr data, it will take into account the longer/heavier bullet. Not like a WC at all. Unless he is feeding an old M10 or such, it should not be an issue, especially since all new loads should be worked up. again, OAL isn't going to come into play like to does in a 9 or 40, where the pressures are easily double & the case volume is half.
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Old 04-23-2017, 09:40 PM
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Just a reminder; there will be no signs of excessive pressure evident in .38 Special loading, or any other caliber of similar pressure (45 ACP, 45 Colt, etc.) except for a cylinder bursting and the top strap hitting the ceiling.
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Old 04-24-2017, 04:50 PM
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According to Lyman, the 358430 bullet has a length from base to cannelure of .412 inches. I just got my 190 grain Hunters Supply LFP today, and I measured the distance from base to cannelure on them, and I got .410 inches to the bottom of the groove. According to the Lyman load data, I feel pretty comfortable starting at the low end and working up. If the seat depth is the same, then all other things being equal but reduced weight, I should have pretty much the same or lower pressure.
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