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BULA FORGED Trigger Group???

This is a discussion on BULA FORGED Trigger Group??? within the Modern M14 forums, part of the M14 M1A Forum category; Lysander, Thanks for that picture, l have been trying to get my head around what a trigger housing forging would look like....


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Old April 17th, 2020, 07:55 AM   #76
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Lysander, Thanks for that picture, l have been trying to get my head around what a trigger housing forging would look like.

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Old April 17th, 2020, 08:24 AM   #77
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The benefit of forging is smaller and more homogeneous grain size, plus fewer inclusions or other defects that could initiate failure. The result of this is that you get slightly higher (like 10%) ultimate tensile strength, better fatigue performance, better impact performance. These are important for highly stressed parts, like triggers and hammers (where the sear tips experience loading up at the ultimate tensile strength of the steel). Or in a receiver, which has the shock loading on the counter lug surfaces.

However I fail to see where this degree of stress is placed on the trigger housing.

The only other area I see that is critical is hole alignment. If the casting has finished holes molded in, is there any warpage in the part that would make your trigger pin and hammer pin not parallel? In a forged part, those holes are machined, so you would assume that if the part is set in the machine properly, the holes are parallel prior to heat treat. In a cast part, you could attempt to cast the holes, or you could cast pilot holes and go back and finish machine them, though the latter option would add cost.

I see hole location as the one thing that has to be right. Machining the holes is the way to do that. Forging requires machining the holes, so these ought to be good. Machined holes does not preclude casting, so it depends.

The only other reason for a forging is consumer demand. USGI parts are the gold standard, these were forged, so consumers want forged. You can fight an expensive and uphill battle to convince consumers that a cast part is just as good (or better), and you may have all the technical data to support that claim. But when you are marketing to people who do not understand the subject, you will not win, so you might as well give consumers what they want.

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Old April 17th, 2020, 08:34 AM   #78
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I have assembled and used plenty of both forged and cast trigger housings from Bula Defense Systems and none have yet broken with use.

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Old April 17th, 2020, 08:36 AM   #79
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I would like to see a video on these on how these parts are forged and the other ways they are cut out.
It would explain more for us to see.

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Old April 17th, 2020, 09:36 AM   #80
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Quote:
Originally Posted by ShootingSight View Post
The benefit of forging is smaller and more homogeneous grain size, plus fewer inclusions or other defects that could initiate failure. The result of this is that you get slightly higher (like 10%) ultimate tensile strength, better fatigue performance, better impact performance. These are important for highly stressed parts, like triggers and hammers (where the sear tips experience loading up at the ultimate tensile strength of the steel). Or in a receiver, which has the shock loading on the counter lug surfaces.

However I fail to see where this degree of stress is placed on the trigger housing.

The only other area I see that is critical is hole alignment. If the casting has finished holes molded in, is there any warpage in the part that would make your trigger pin and hammer pin not parallel? In a forged part, those holes are machined, so you would assume that if the part is set in the machine properly, the holes are parallel prior to heat treat. In a cast part, you could attempt to cast the holes, or you could cast pilot holes and go back and finish machine them, though the latter option would add cost.

I see hole location as the one thing that has to be right. Machining the holes is the way to do that. Forging requires machining the holes, so these ought to be good. Machined holes does not preclude casting, so it depends.

The only other reason for a forging is consumer demand. USGI parts are the gold standard, these were forged, so consumers want forged. You can fight an expensive and uphill battle to convince consumers that a cast part is just as good (or better), and you may have all the technical data to support that claim. But when you are marketing to people who do not understand the subject, you will not win, so you might as well give consumers what they want.
There is one other reason to forge parts: to achieve near net shape at lower cost than casting.

The front sight base of the M16/M4 is a forging. (It is the only forged steel part in and M16/M4.) Because of its shape and the required machining, it would take the same machine time, cast or forged. So, the speed at which you can forge them actually makes them cheaper for high volume production.

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The result of this is that you get slightly higher (like 10%) ultimate tensile strength, better fatigue performance, better impact performance.
This is a bit incorrect and a bit of an over-simplification.

The ultimate strength of a forging is not increased. The yield strength, and the other properties noted, are increased in the longitudinal direction only, and the amount of increase varies in relation to the percent elongated.

But, you never get something for nothing. Some transverse properties are reduced.

http://www.dropforging.net/how-does-...structure.html
Quote:
However, we should be clear that not all of the mechanical properties will vary significantly with the grain flow. For example, strength and hardness are primarily controlled by the alloy chemistry and the heat treatment that is given to the forging. Grain flow will not have a major effect on the strength or the hardness of the alloy.
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Last edited by lysander; April 17th, 2020 at 10:18 AM.
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Old April 17th, 2020, 02:40 PM   #81
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The raw forging is done at Bula Forge and Machine using forging press and their dies. They make the dies there too. Then they machine them. The forgings are similar to the examples given but are solid where the guts go. I think I showed Art the forgings when he visited Bula last summer. Anyway, no more need for speculation as to how they are done. Would like to see more parts made because I need to build!!

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Old April 17th, 2020, 02:47 PM   #82
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Originally Posted by deuceguy View Post
The raw forging is done at Bula Forge and Machine using forging press and their dies. They make the dies there too. Then they machine them. The forgings are similar to the examples given but are solid where the guts go. I think I showed Art the forgings when he visited Bula last summer. Anyway, no more need for speculation as to how they are done. Would like to see more parts made because I need to build!!
I would love to tour the Bula facility the next time I come home to visit the family. Would this be possible deuceguy?

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Old April 17th, 2020, 04:52 PM   #83
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I don't know if they give tours anymore. I left Bula in December.

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Old April 17th, 2020, 08:24 PM   #84
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Lysander, you are talking about grain alignment only.

The other benefits of wrought steel are that there are fewer inclusions, stringers, so fewer sites for cracks to originate. That is why UTS is slightly higher. Further, you get smaller grains on average, which retards crack initiation at an inclusion, so fatigue performance is better.

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Old April 17th, 2020, 09:02 PM   #85
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Quote:
Originally Posted by ShootingSight View Post
Lysander, you are talking about grain alignment only.

The other benefits of wrought steel are that there are fewer inclusions, stringers, so fewer sites for cracks to originate. That is why UTS is slightly higher. Further, you get smaller grains on average, which retards crack initiation at an inclusion, so fatigue performance is better.
In the longitudinal direction only.

Fatigue resistance can be gauged by impact energy, elongation and area reduction.

From the link: (Which, BTW, is from an article published by the forging industry's own magazine.)
Quote:


Note the major increase in properties that are associated with a crack/fracture formation and propagation through the test sample. The yield strength is reasonably constant.
If you look at how (good) forgings are done, the loading is always in the longitudinal direction.

There is a report from Springfield on this very subject, titled Tensile and Impact properties of Investment Cast Steels. Rough castings and forging of standard tensile test bars were made and finish machined to tensile test bars, and tested. The results:


You can see that it is alloy dependent, ie some alloys cast better than others, but casting is not always weaker.

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